dist/common/EncoreBootImage.cpp

/*
 * File:  EncoreBootImage.cpp
 *
 * Copyright (c) Freescale Semiconductor, Inc. All rights reserved.
 * See included license file for license details.
 */

#include "EncoreBootImage.h"
#include <stdexcept>
#include <algorithm>
#include <time.h>
#include "crc.h"
#include "SHA1.h"
#include "Random.h"
#include "rijndael.h"
#include "RijndaelCBCMAC.h"
#include "Logging.h"
#include "EndianUtilities.h"

using namespace elftosb;

EncoreBootImage::EncoreBootImage()
:         m_headerFlags(0),
          m_productVersion(),
          m_componentVersion(),
          m_driveTag(0)
{
}

EncoreBootImage::~EncoreBootImage()
{
          // dispose of all sections
          section_iterator_t it = beginSection();
          for (; it != endSection(); ++it)
          {
                    delete *it;
          }
}

//! \exception std::runtime_error Raised if \a newSection has the same tag as a previously
//!                 added section.
void EncoreBootImage::addSection(Section * newSection)
{
          // check for another section with this tag
          section_iterator_t it = beginSection();
          for (; it != endSection(); ++it)
          {
                    if ((*it)->getIdentifier() == newSection->getIdentifier())
                    {
                              throw std::runtime_error("new section with non-unique tag");
                    }
          }

          // no conflicting section tags, so add it
          m_sections.push_back(newSection);

          // tell the image who owns it now
          newSection->setImage(this);
}

EncoreBootImage::section_iterator_t EncoreBootImage::findSection(Section * section)
{
          return std::find(beginSection(), endSection(), section);
}

void EncoreBootImage::setProductVersion(const version_t & version)
{
          m_productVersion = version;
}

void EncoreBootImage::setComponentVersion(const version_t & version)
{
          m_componentVersion = version;
}

//! \todo Optimize writing section data. Right now it only writes one block at a
//!                 time, which is of course quite slow (in relative terms).
//!       \todo Refactor this into several different methods for writing each region
//!                 of the image. Use a context structure to keep track of shared data between
//!                 each of the methods.
//! \todo Refactor the section and boot tag writing code to only have a single
//!                 copy of the block writing and encryption loop.
void EncoreBootImage::writeToStream(std::ostream & stream)
{
          // always generate the session key or DEK even if image is unencrypted
          m_sessionKey.randomize();

          // prepare to compute CBC-MACs with each KEK
          unsigned i;
          smart_array_ptr<RijndaelCBCMAC> macs(0);
          if (isEncrypted())
          {
                    macs = new RijndaelCBCMAC[m_keys.size()];
                    for (i=0; i < m_keys.size(); ++i)
                    {
                              RijndaelCBCMAC mac(m_keys[i]);
                              (macs.get())[i] = mac;
                    }
          }

          // prepare to compute SHA-1 digest over entire image
          CSHA1 hash;
          hash.Reset();

          // count of total blocks written to the file
          unsigned fileBlocksWritten = 0;

          // we need some pieces of the header down below
          boot_image_header_t imageHeader;
          prepareImageHeader(imageHeader);

          // write plaintext header
          {
                    // write header
                    assert(sizeOfPaddingForCipherBlocks(sizeof(boot_image_header_t)) == 0);
                    stream.write(reinterpret_cast<char *>(&imageHeader), sizeof(imageHeader));
                    fileBlocksWritten += numberOfCipherBlocks(sizeof(imageHeader));

                    // update CBC-MAC over image header
                    if (isEncrypted())
                    {
                              for (i=0; i < m_keys.size(); ++i)
                              {
                                        (macs.get())[i].update(reinterpret_cast<uint8_t *>(&imageHeader), sizeof(imageHeader));
                              }
                    }

                    // update SHA-1
                    hash.Update(reinterpret_cast<uint8_t *>(&imageHeader), sizeof(imageHeader));
          }

          // write plaintext section table
          {
                    section_iterator_t it = beginSection();
                    for (; it != endSection(); ++it)
                    {
                              Section * section = *it;

                              // write header for this section
                              assert(sizeOfPaddingForCipherBlocks(sizeof(section_header_t)) == 0);
                              section_header_t sectionHeader;
                              section->fillSectionHeader(sectionHeader);
                              stream.write(reinterpret_cast<char *>(&sectionHeader), sizeof(sectionHeader));
                              fileBlocksWritten += numberOfCipherBlocks(sizeof(sectionHeader));

                              // update CBC-MAC over this entry
                              if (isEncrypted())
                              {
                                        for (i=0; i < m_keys.size(); ++i)
                                        {
                                                  (macs.get())[i].update(reinterpret_cast<uint8_t *>(&sectionHeader), sizeof(sectionHeader));
                                        }
                              }

                              // update SHA-1
                              hash.Update(reinterpret_cast<uint8_t *>(&sectionHeader), sizeof(sectionHeader));
                    }
          }

          // finished with the CBC-MAC
          if (isEncrypted())
          {
                    for (i=0; i < m_keys.size(); ++i)
                    {
                              (macs.get())[i].finalize();
                    }
          }

          // write key dictionary
          if (isEncrypted())
          {
                    key_iterator_t it = beginKeys();
                    for (i=0; it != endKeys(); ++it, ++i)
                    {
                              // write CBC-MAC result for this key, then update SHA-1
                              RijndaelCBCMAC & mac = (macs.get())[i];
                              const RijndaelCBCMAC::block_t & macResult = mac.getMAC();
                              stream.write(reinterpret_cast<const char *>(&macResult), sizeof(RijndaelCBCMAC::block_t));
                              hash.Update(reinterpret_cast<const uint8_t *>(&macResult), sizeof(RijndaelCBCMAC::block_t));
                              fileBlocksWritten++;

                              // encrypt DEK with this key, write it out, and update image digest
                              Rijndael cipher;
                              cipher.init(Rijndael::CBC, Rijndael::Encrypt, *it, Rijndael::Key16Bytes, imageHeader.m_iv);
                              AESKey<128>::key_t wrappedSessionKey;
                              cipher.blockEncrypt(m_sessionKey, sizeof(AESKey<128>::key_t) * 8, wrappedSessionKey);
                              stream.write(reinterpret_cast<char *>(&wrappedSessionKey), sizeof(wrappedSessionKey));
                              hash.Update(reinterpret_cast<uint8_t *>(&wrappedSessionKey), sizeof(wrappedSessionKey));
                              fileBlocksWritten++;
                    }
          }

          // write sections and boot tags
          {
                    section_iterator_t it = beginSection();
                    for (; it != endSection(); ++it)
                    {
                              section_iterator_t itCopy = it;
                              bool isLastSection = (++itCopy == endSection());

                              Section * section = *it;
                              cipher_block_t block;
                              unsigned blockCount = section->getBlockCount();
                              unsigned blocksWritten = 0;

                              Rijndael cipher;
                              cipher.init(Rijndael::CBC, Rijndael::Encrypt, m_sessionKey, Rijndael::Key16Bytes, imageHeader.m_iv);

                              // Compute the number of padding blocks needed to align the section. This first
                              // call to getPadBlockCountForOffset() passes an offset that excludes
                              // the boot tag for this section.
                              unsigned paddingBlocks = getPadBlockCountForSection(section, fileBlocksWritten);

                              // Insert nop commands as padding to align the start of the section, if
                              // the section has special alignment requirements.
                              NopCommand nop;
                              while (paddingBlocks--)
                              {
                                        blockCount = nop.getBlockCount();
                                        blocksWritten = 0;
                                        while (blocksWritten < blockCount)
                                        {
                                                  nop.getBlocks(blocksWritten, 1, &block);

                                                  if (isEncrypted())
                                                  {
                                                            // re-init after encrypt to update IV
                                                            cipher.blockEncrypt(block, sizeof(cipher_block_t) * 8, block);
                                                            cipher.init(Rijndael::CBC, Rijndael::Encrypt, m_sessionKey, Rijndael::Key16Bytes, block);
                                                  }

                                                  stream.write(reinterpret_cast<char *>(&block), sizeof(cipher_block_t));
                                                  hash.Update(reinterpret_cast<uint8_t *>(&block), sizeof(cipher_block_t));

                                                  blocksWritten++;
                                                  fileBlocksWritten++;
                                        }
                              }

                              // reinit cipher for boot tag
                              cipher.init(Rijndael::CBC, Rijndael::Encrypt, m_sessionKey, Rijndael::Key16Bytes, imageHeader.m_iv);

                              // write boot tag
                              TagCommand tag(*section);
                              tag.setLast(isLastSection);
                              if (!isLastSection)
                              {
                                        // If this isn't the last section, the tag needs to include any
                                        // padding for the next section in its length, otherwise the ROM
                                        // won't be able to find the next section's boot tag.
                                        unsigned nextSectionOffset = fileBlocksWritten + section->getBlockCount() + 1;
                                        tag.setSectionLength(section->getBlockCount() + getPadBlockCountForSection(*itCopy, nextSectionOffset));
                              }
                              blockCount = tag.getBlockCount();
                              blocksWritten = 0;
                              while (blocksWritten < blockCount)
                              {
                                        tag.getBlocks(blocksWritten, 1, &block);

                                        if (isEncrypted())
                                        {
                                                  // re-init after encrypt to update IV
                                                  cipher.blockEncrypt(block, sizeof(cipher_block_t) * 8, block);
                                                  cipher.init(Rijndael::CBC, Rijndael::Encrypt, m_sessionKey, Rijndael::Key16Bytes, block);
                                        }

                                        stream.write(reinterpret_cast<char *>(&block), sizeof(cipher_block_t));
                                        hash.Update(reinterpret_cast<uint8_t *>(&block), sizeof(cipher_block_t));

                                        blocksWritten++;
                                        fileBlocksWritten++;
                              }

                              // reinit cipher for section data
                              cipher.init(Rijndael::CBC, Rijndael::Encrypt, m_sessionKey, Rijndael::Key16Bytes, imageHeader.m_iv);

                              // write section data
                              blockCount = section->getBlockCount();
                              blocksWritten = 0;
                              while (blocksWritten < blockCount)
                              {
                                        section->getBlocks(blocksWritten, 1, &block);

                                        // Only encrypt the section contents if the entire boot image is encrypted
                                        // and the section doesn't have the "leave unencrypted" flag set. Even if the
                                        // section is unencrypted the boot tag will remain encrypted.
                                        if (isEncrypted() && !section->getLeaveUnencrypted())
                                        {
                                                  // re-init after encrypt to update IV
                                                  cipher.blockEncrypt(block, sizeof(cipher_block_t) * 8, block);
                                                  cipher.init(Rijndael::CBC, Rijndael::Encrypt, m_sessionKey, Rijndael::Key16Bytes, block);
                                        }

                                        stream.write(reinterpret_cast<char *>(&block), sizeof(cipher_block_t));
                                        hash.Update(reinterpret_cast<uint8_t *>(&block), sizeof(cipher_block_t));

                                        blocksWritten++;
                                        fileBlocksWritten++;
                              }
                    }
          }

          // write SHA-1 digest over entire image
          {
                    // allocate enough room for digest and bytes to pad out to the next cipher block
                    const unsigned padBytes = sizeOfPaddingForCipherBlocks(sizeof(sha1_digest_t));
                    unsigned digestBlocksSize = sizeof(sha1_digest_t) + padBytes;
                    smart_array_ptr<uint8_t> digestBlocks = new uint8_t[digestBlocksSize];
                    hash.Final();
                    hash.GetHash(digestBlocks.get());

                    // set the pad bytes to random values
                    RandomNumberGenerator rng;
                    rng.generateBlock(&(digestBlocks.get())[sizeof(sha1_digest_t)], padBytes);

                    // encrypt with session key
                    if (isEncrypted())
                    {
                              Rijndael cipher;
                              cipher.init(Rijndael::CBC, Rijndael::Encrypt, m_sessionKey, Rijndael::Key16Bytes, imageHeader.m_iv);
                              cipher.blockEncrypt(digestBlocks.get(), digestBlocksSize * 8, digestBlocks.get());
                    }

                    // write to the stream
                    stream.write(reinterpret_cast<char *>(digestBlocks.get()), digestBlocksSize);
          }
}

void EncoreBootImage::prepareImageHeader(boot_image_header_t & header)
{
          // get identifier for the first bootable section
          Section * firstBootSection = findFirstBootableSection();
          section_id_t firstBootSectionID = 0;
          if (firstBootSection)
          {
                    firstBootSectionID = firstBootSection->getIdentifier();
          }

          // fill in header fields
          header.m_signature[0] = 'S';
          header.m_signature[1] = 'T';
          header.m_signature[2] = 'M';
          header.m_signature[3] = 'P';
          header.m_majorVersion = ROM_BOOT_IMAGE_MAJOR_VERSION;
          header.m_minorVersion = ROM_BOOT_IMAGE_MINOR_VERSION;
          header.m_flags = ENDIAN_HOST_TO_LITTLE_U16(m_headerFlags);
          header.m_imageBlocks = ENDIAN_HOST_TO_LITTLE_U32(getImageSize());
          header.m_firstBootableSectionID = ENDIAN_HOST_TO_LITTLE_U32(firstBootSectionID);
          header.m_keyCount = ENDIAN_HOST_TO_LITTLE_U16((uint16_t)m_keys.size());
          header.m_headerBlocks = ENDIAN_HOST_TO_LITTLE_U16((uint16_t)numberOfCipherBlocks(sizeof(header)));
          header.m_sectionCount = ENDIAN_HOST_TO_LITTLE_U16((uint16_t)m_sections.size());
          header.m_sectionHeaderSize = ENDIAN_HOST_TO_LITTLE_U16((uint16_t)numberOfCipherBlocks(sizeof(section_header_t)));
          header.m_signature2[0] = 's';
          header.m_signature2[1] = 'g';
          header.m_signature2[2] = 't';
          header.m_signature2[3] = 'l';
          header.m_timestamp = ENDIAN_HOST_TO_LITTLE_U64(getTimestamp());
          header.m_driveTag = m_driveTag;

          // Prepare version fields by converting them to the correct byte order.
          header.m_productVersion = m_productVersion;
          header.m_componentVersion = m_componentVersion;
          header.m_productVersion.fixByteOrder();
          header.m_componentVersion.fixByteOrder();

          // the fields are dependant on others
          header.m_keyDictionaryBlock = ENDIAN_HOST_TO_LITTLE_U16(header.m_headerBlocks + header.m_sectionCount * header.m_sectionHeaderSize);
          header.m_firstBootTagBlock = ENDIAN_HOST_TO_LITTLE_U32(header.m_keyDictionaryBlock + header.m_keyCount * 2);

          // generate random pad bytes
          RandomNumberGenerator rng;
          rng.generateBlock(header.m_padding0, sizeof(header.m_padding0));
          rng.generateBlock(header.m_padding1, sizeof(header.m_padding1));

          // compute SHA-1 digest over the image header
          uint8_t * message = reinterpret_cast<uint8_t *>(&header.m_signature);
          uint32_t length = static_cast<uint32_t>(sizeof(header) - sizeof(header.m_digest)); // include padding

          CSHA1 hash;
          hash.Reset();
          hash.Update(message, length);
          hash.Final();
          hash.GetHash(header.m_digest);
}

//! Returns the number of microseconds since 00:00 1-1-2000. In actuality, the timestamp
//! is only accurate to seconds, and is simply extended out to microseconds.
//!
//! \todo Use the operating system's low-level functions to get a true microsecond
//!                 timestamp, instead of faking it like we do now.
//! \bug The timestamp might be off an hour.
uint64_t EncoreBootImage::getTimestamp()
{
#if defined(WIN32) || defined(__CYGWIN__) || defined(__sun)
          struct tm epoch = { 0, 0, 0, 1, 0, 100, 0, 0 }; // 00:00 1-1-2000
#else
          struct tm epoch = { 0, 0, 0, 1, 0, 100, 0, 0, 1, 0, NULL }; // 00:00 1-1-2000
#endif
          time_t epochTime = mktime(&epoch);
          time_t now = time(NULL);
          now -= epochTime;
          uint64_t microNow = uint64_t(now) * 1000000;      // convert to microseconds
          return microNow;
}

//! Scans the section list looking for the first section which has
//! the #ROM_SECTION_BOOTABLE flag set on it.
EncoreBootImage::Section * EncoreBootImage::findFirstBootableSection()
{
          section_iterator_t it = beginSection();
          for (; it != endSection(); ++it)
          {
                    if ((*it)->getFlags() & ROM_SECTION_BOOTABLE)
                    {
                              return *it;
                    }
          }

          // no bootable sections were found
          return NULL;
}

//! The boot tag for \a section is taken into account, thus making the
//! result offset point to the first block of the actual section data.
//!
//! \note The offset will only be valid if all encryption keys and all
//! sections have already been added to the image.
uint32_t EncoreBootImage::getSectionOffset(Section * section)
{
          // start with boot image headers
          uint32_t offset = numberOfCipherBlocks(sizeof(boot_image_header_t));  // header
          offset += numberOfCipherBlocks(sizeof(section_header_t)) * sectionCount();      // section table
          offset += 2 * keyCount();     // key dictiontary

          // add up sections before this one
          section_iterator_t it = beginSection();
          for (; it != endSection() && *it != section; ++it)
          {
                    Section * thisSection = *it;

                    // insert padding for section alignment
                    offset += getPadBlockCountForSection(thisSection, offset);

                    // add one for boot tag associated with this section
                    offset++;

                    // now add the section's contents
                    offset += thisSection->getBlockCount();
          }

          // and add padding for this section
          offset += getPadBlockCountForSection(section, offset);

          // skip over this section's boot tag
          offset++;

          return offset;
}

//! Computes the number of blocks of padding required to align \a section while
//! taking into account the boot tag that gets inserted before the section contents.
unsigned EncoreBootImage::getPadBlockCountForSection(Section * section, unsigned offset)
{
          // Compute the number of padding blocks needed to align the section. This first
          // call to getPadBlockCountForOffset() passes an offset that excludes
          // the boot tag for this section.
          unsigned paddingBlocks = section->getPadBlockCountForOffset(offset);

          // If the pad count comes back as 0 then we need to try again with an offset that
          // includes the boot tag. This is all because we're aligning the section contents
          // start and not the section's boot tag.
          if (paddingBlocks == 0)
          {
                    paddingBlocks = section->getPadBlockCountForOffset(offset + 1);
          }
          // Otherwise if we get a nonzero pad amount then we need to subtract the block
          // for the section's boot tag from the pad count.
          else
          {
                    paddingBlocks--;
          }

          return paddingBlocks;
}

uint32_t EncoreBootImage::getImageSize()
{
          // determine to total size of the image
          const uint32_t headerBlocks = numberOfCipherBlocks(sizeof(boot_image_header_t));
          const uint32_t sectionHeaderSize = numberOfCipherBlocks(sizeof(section_header_t));
          uint32_t imageBlocks = headerBlocks;
          imageBlocks += sectionHeaderSize * m_sections.size();       // section table
          imageBlocks += 2 * m_keys.size();       // key dict

          // add in each section's size
          section_iterator_t it = beginSection();
          for (; it != endSection(); ++it)
          {
                    // add in this section's size, padding to align it, and its boot tag
                    imageBlocks += getPadBlockCountForSection(*it, imageBlocks);
                    imageBlocks += (*it)->getBlockCount();
                    imageBlocks++;
          }

          // image MAC
          imageBlocks += 2;

          return imageBlocks;
}

void EncoreBootImage::debugPrint() const
{
          const_section_iterator_t it = beginSection();
          for (; it != endSection(); ++it)
          {
                    const Section * section = *it;
                    section->debugPrint();
          }
}

//! \param blocks Pointer to the raw data blocks.
//! \param count Number of blocks pointed to by \a blocks.
//! \param[out] consumed On exit, this points to the number of cipher blocks that were occupied
//!                 by the command. Should be at least 1 for every command. This must not be NULL
//!                 on entry!
//!
//! \return A new boot command instance.
//! \retval NULL The boot command pointed to by \a blocks was not recognized as a known
//!     command type.
//!
//! \exception std::runtime_error This exception indicates that a command was recognized
//!     but contained invalid data. Compare this to a NULL result which indicates that
//!     no command was recognized at all.
EncoreBootImage::BootCommand * EncoreBootImage::BootCommand::createFromData(const cipher_block_t * blocks, unsigned count, unsigned * consumed)
{
          const boot_command_t * header = reinterpret_cast<const boot_command_t *>(blocks);
    BootCommand * command = NULL;

    switch (header->m_tag)
    {
        case ROM_NOP_CMD:
            command = new NopCommand();
            break;
        case ROM_TAG_CMD:
            command = new TagCommand();
            break;
        case ROM_LOAD_CMD:
            command = new LoadCommand();
            break;
        case ROM_FILL_CMD:
            command = new FillCommand();
            break;
        case ROM_MODE_CMD:
            command = new ModeCommand();
            break;
        case ROM_JUMP_CMD:
            command = new JumpCommand();
            break;
        case ROM_CALL_CMD:
            command = new CallCommand();
            break;
    }

    if (command)
    {
        command->initFromData(blocks, count, consumed);
    }
    return command;
}

//! The checksum algorithm is totally straightforward, except that the
//! initial checksum byte value is set to 0x5a instead of 0.
uint8_t EncoreBootImage::BootCommand::calculateChecksum(const boot_command_t & header)
{
          const uint8_t * bytes = reinterpret_cast<const uint8_t *>(&header);
          uint8_t checksum = 0x5a;
          int i;

          // start at one to skip checksum field
          for (i = 1; i < sizeof(header); ++i)
          {
                    checksum += bytes[i];
          }

          return checksum;
}

//! The default implementation returns 0, indicating that no blocks are
//! available.
unsigned EncoreBootImage::BootCommand::getBlockCount() const
{
          return 1 + getDataBlockCount();
}

//! Up to \a maxCount cipher blocks are copied into the buffer pointed to by
//! the \a data argument. The index of the first block to copy is
//! held in the \a offset argument.
//!
//! \param offset Starting block number to copy. Zero means the first available block.
//! \param maxCount Up to this number of blocks may be copied into \a data. Must be 1 or greater.
//! \param data Buffer for outgoing cipher blocks. Must have enough room to hold
//!                 \a maxCount blocks.
//!
//! \return The number of cipher blocks copied into \a data.
//! \retval 0 No more blocks are available and nothing was written to \a data.
//!
//! \exception std::out_of_range If \a offset is invalid.
unsigned EncoreBootImage::BootCommand::getBlocks(unsigned offset, unsigned maxCount, cipher_block_t * data)
{
          assert(data);
          assert(maxCount >= 1);

          // check for valid offset
          if (offset >= getBlockCount())
          {
                    throw std::out_of_range("invalid offset");
          }

          // handle the command header block separately
          if (offset == 0)
          {
                    assert(sizeof(boot_command_t) == sizeof(cipher_block_t));

                    boot_command_t header;
                    fillCommandHeader(header);
                    memcpy(data, &header, sizeof(header));

                    return 1;
          }

          // handle any data blocks
          return getDataBlocks(offset - 1, maxCount, data);
}

//! The checksum field of \a testHeader is always computed and checked against itself.
//! All other fields are compared to the corresponding value set in \a modelHeader
//! if the appropriate flag is set in \a whichFields. For example, the m_address fields
//! in \a testHeader and \a modelHeader are compared when the CMD_ADDRESS_FIELD bit
//! is set in \a whichFields. An exception is thrown if any comparison fails.
//!
//! \param modelHeader The baseline header to compare against. Only those fields that
//!                 have corresponding bits set in \a whichFields need to be set.
//! \param testHeader The actual command header which is being validated.
//! \param whichFields A bitfield used to determine which fields of the boot command
//!                 header are compared. Possible values are:
//!                           - CMD_TAG_FIELD
//!                           - CMD_FLAGS_FIELD
//!                           - CMD_ADDRESS_FIELD
//!                           - CMD_COUNT_FIELD
//!                           - CMD_DATA_FIELD
//!
//! \exception std::runtime_error Thrown if any requested validation fails.
void EncoreBootImage::BootCommand::validateHeader(const boot_command_t * modelHeader, const boot_command_t * testHeader, unsigned whichFields)
{
          // compare all the fields that were requested
          if ((whichFields & CMD_TAG_FIELD) && (testHeader->m_tag != modelHeader->m_tag))
          {
                    throw std::runtime_error("invalid tag field");
          }

          if ((whichFields & CMD_FLAGS_FIELD) && (testHeader->m_flags != modelHeader->m_flags))
          {
                    throw std::runtime_error("invalid flags field");
          }

          if ((whichFields & CMD_ADDRESS_FIELD) && (testHeader->m_address != modelHeader->m_address))
          {
                    throw std::runtime_error("invalid address field");
          }

          if ((whichFields & CMD_COUNT_FIELD) && (testHeader->m_count != modelHeader->m_count))
          {
                    throw std::runtime_error("invalid count field");
          }

          if ((whichFields & CMD_DATA_FIELD) && (testHeader->m_data != modelHeader->m_data))
          {
                    throw std::runtime_error("invalid data field");
          }

          // calculate checksum
          uint8_t testChecksum = calculateChecksum(*testHeader);
          if (testChecksum != testHeader->m_checksum)
          {
                    throw std::runtime_error("invalid checksum");
          }
}

//! Since the NOP command has no data, this method just validates the command header.
//! All fields except the checksum are expected to be set to 0.
//!
//! \param blocks Pointer to the raw data blocks.
//! \param count Number of blocks pointed to by \a blocks.
//! \param[out] consumed On exit, this points to the number of cipher blocks that were occupied
//!                 by the command. Should be at least 1 for every command. This must not be NULL
//!                 on entry!
//!
//! \exception std::runtime_error Thrown if header fields are invalid.
void EncoreBootImage::NopCommand::initFromData(const cipher_block_t * blocks, unsigned count, unsigned * consumed)
{
          const boot_command_t model = { 0, ROM_NOP_CMD, 0, 0, 0, 0 };
          const boot_command_t * header = reinterpret_cast<const boot_command_t *>(blocks);
          validateHeader(&model, header, CMD_TAG_FIELD | CMD_FLAGS_FIELD | CMD_ADDRESS_FIELD | CMD_COUNT_FIELD | CMD_DATA_FIELD);

          *consumed = 1;
}

//! All fields of the boot command header structure are set to 0, except
//! for the checksum. This includes the tag field since the tag value for
//! the #ROM_NOP_CMD is zero. And since all fields are zeroes the checksum
//! remains the initial checksum value of 0x5a.
void EncoreBootImage::NopCommand::fillCommandHeader(boot_command_t & header)
{
          header.m_tag = getTag();
          header.m_flags = 0;
          header.m_address = 0;
          header.m_count = 0;
          header.m_data = 0;
          header.m_checksum = calculateChecksum(header);    // do this last
}

void EncoreBootImage::NopCommand::debugPrint() const
{
          Log::log(Logger::INFO2, "\tNOOP\n");
}

//! The identifier, length, and flags fields are taken from \a section.
//!
//! \todo How does length get set correctly if the length is supposed to include
//!                 this command?
EncoreBootImage::TagCommand::TagCommand(const Section & section)
{
          m_sectionIdentifier = section.getIdentifier();
          m_sectionLength = section.getBlockCount();
          m_sectionFlags = section.getFlags();
}

//! \param blocks Pointer to the raw data blocks.
//! \param count Number of blocks pointed to by \a blocks.
//! \param[out] consumed On exit, this points to the number of cipher blocks that were occupied
//!                 by the command. Should be at least 1 for every command. This must not be NULL
//!                 on entry!
//!
//! \exception std::runtime_error Thrown if header fields are invalid.
void EncoreBootImage::TagCommand::initFromData(const cipher_block_t * blocks, unsigned count, unsigned * consumed)
{
          const boot_command_t model = { 0, ROM_TAG_CMD, 0, 0, 0, 0 };
          const boot_command_t * header = reinterpret_cast<const boot_command_t *>(blocks);
          validateHeader(&model, header, CMD_TAG_FIELD);

    // read fields from header
          m_isLast = (ENDIAN_LITTLE_TO_HOST_U16(header->m_flags) & ROM_LAST_TAG) != 0;
          m_sectionIdentifier = ENDIAN_LITTLE_TO_HOST_U32(header->m_address);
          m_sectionLength = ENDIAN_LITTLE_TO_HOST_U32(header->m_count);
          m_sectionFlags = ENDIAN_LITTLE_TO_HOST_U32(header->m_data);

          *consumed = 1;
}

//! This method currently assumes that the next tag command will come immediately
//! after the data for this section.
void EncoreBootImage::TagCommand::fillCommandHeader(boot_command_t & header)
{
          header.m_tag = getTag();
          header.m_flags = ENDIAN_HOST_TO_LITTLE_U16(m_isLast ? ROM_LAST_TAG : 0);
          header.m_address = ENDIAN_HOST_TO_LITTLE_U32(m_sectionIdentifier);
          header.m_count = ENDIAN_HOST_TO_LITTLE_U32(m_sectionLength);
          header.m_data = ENDIAN_HOST_TO_LITTLE_U32(m_sectionFlags);
          header.m_checksum = calculateChecksum(header);    // do this last
}

void EncoreBootImage::TagCommand::debugPrint() const
{
          Log::log(Logger::INFO2, "  BTAG | sec=0x%08x | cnt=0x%08x | flg=0x%08x\n", m_sectionIdentifier, m_sectionLength, m_sectionFlags);
}

//! All fields are set to zero.
//!
EncoreBootImage::LoadCommand::LoadCommand()
:         BootCommand(), m_data(), m_padCount(0), m_length(0), m_address(0), m_loadDCD(false)
{
          fillPadding();
}

EncoreBootImage::LoadCommand::LoadCommand(uint32_t address, const uint8_t * data, uint32_t length)
:         BootCommand(), m_data(), m_padCount(0), m_length(0), m_address(address), m_loadDCD(false)
{
          fillPadding();
          setData(data, length);
}

//! \param blocks Pointer to the raw data blocks.
//! \param count Number of blocks pointed to by \a blocks.
//! \param[out] consumed On exit, this points to the number of cipher blocks that were occupied
//!                 by the command. Should be at least 1 for every command. This must not be NULL
//!                 on entry!
//!
//! \exception std::runtime_error This exception is thrown if the actual CRC of the load
//!     data does not match the CRC stored in the command header. Also thrown if the
//!     \a count parameter is less than the number of data blocks needed for the length
//!     specified in the command header or if header fields are invalid.
void EncoreBootImage::LoadCommand::initFromData(const cipher_block_t * blocks, unsigned count, unsigned * consumed)
{
    // check static fields
          const boot_command_t model = { 0, ROM_LOAD_CMD, 0, 0, 0, 0 };
          const boot_command_t * header = reinterpret_cast<const boot_command_t *>(blocks);
          validateHeader(&model, header, CMD_TAG_FIELD);

    // read fields from header
          m_address = ENDIAN_LITTLE_TO_HOST_U32(header->m_address);
          m_length = ENDIAN_LITTLE_TO_HOST_U32(header->m_count);
    unsigned crc = ENDIAN_LITTLE_TO_HOST_U32(header->m_data);
    unsigned dataBlockCount = numberOfCipherBlocks(m_length);
    m_padCount = sizeOfPaddingForCipherBlocks(dataBlockCount);
          m_loadDCD = (ENDIAN_LITTLE_TO_HOST_U16(header->m_flags) & ROM_LOAD_DCD) != 0;

    // make sure there are enough blocks
    if (count - 1 < dataBlockCount)
    {
        throw std::runtime_error("not enough cipher blocks for load data");
    }

    // copy data
    setData(reinterpret_cast<const uint8_t *>(blocks + 1), m_length);

    // copy padding
    if (m_padCount)
    {
        const uint8_t * firstPadByte = reinterpret_cast<const uint8_t *> (blocks + (1 + dataBlockCount)) - m_padCount;
        memcpy(m_padding, firstPadByte, m_padCount);
    }

    // check CRC
    uint32_t actualCRC = calculateCRC();
    if (actualCRC != crc)
    {
        throw std::runtime_error("load data failed CRC check");
    }

          *consumed = 1 + dataBlockCount;
}

//! The only thing unique in the load command header is the
//! #elftosb::EncoreBootImage::boot_command_t::m_data. It contains a CRC-32 over the
//! load data, plus any bytes of padding in the last data cipher block.
void EncoreBootImage::LoadCommand::fillCommandHeader(boot_command_t & header)
{
          header.m_tag = getTag();
          header.m_flags = ENDIAN_HOST_TO_LITTLE_U16(m_loadDCD ? ROM_LOAD_DCD : 0);
          header.m_address = ENDIAN_HOST_TO_LITTLE_U32(m_address);
          header.m_count = ENDIAN_HOST_TO_LITTLE_U32(m_length);
          header.m_data = ENDIAN_HOST_TO_LITTLE_U32(calculateCRC());

          // do this last
          header.m_checksum = calculateChecksum(header);
}

//! A CRC-32 is calculated over the load data, including any pad bytes
//! that are required in the last data cipher block. Including the
//! pad bytes in the CRC makes it vastly easier for the ROM to calculate
//! the CRC for validation.
uint32_t EncoreBootImage::LoadCommand::calculateCRC() const
{
          uint32_t result;
          CRC32 crc;
          crc.update(m_data, m_length);
          if (m_padCount)
          {
                    // include random padding in the CRC
                    crc.update(m_padding, m_padCount);
          }
          crc.truncatedFinal(reinterpret_cast<uint8_t*>(&result), sizeof(result));

          return result;
}

//! A local copy of the load data is made. This copy will be disposed of when this object
//! is destroyed. This means the caller is free to deallocate \a data after this call
//! returns. It also means the caller can pass a pointer into the middle of a buffer for
//! \a data and not worry about ownership issues.
void EncoreBootImage::LoadCommand::setData(const uint8_t * data, uint32_t length)
{
          assert(data);
          assert(length);

          uint8_t * dataCopy = new uint8_t[length];
          memcpy(dataCopy, data, length);

          m_data = dataCopy;
          m_length = length;

          m_padCount = sizeOfPaddingForCipherBlocks(m_length);
}

//! \return The number of cipher blocks required to hold the load data,
//!                 rounded up as necessary.
unsigned EncoreBootImage::LoadCommand::getDataBlockCount() const
{
          // round up to the next cipher block
          return numberOfCipherBlocks(m_length);
}

//! Up to \a maxCount data blocks are copied into the buffer pointed to by
//! the \a data argument. This is only a request for \a maxCount blocks.
//! A return value of 0 indicates that no more blocks are available. The
//! index of the first block to copy is held in the \a offset argument.
//! If there are pad bytes needed to fill out the last data block, they
//! will be filled with random data in order to add to the "whiteness" of
//! the data on both sides of encryption.
//!
//! \param offset Starting block number to copy. Zero means the first available block.
//! \param maxCount Up to this number of blocks may be copied into \a data. Must be 1 or greater.
//! \param data Buffer for outgoing data blocks. Must have enough room to hold
//!                 \a maxCount blocks.
//!
//! \return The number of data blocks copied into \a data.
//! \retval 0 No more blocks are available and nothing was written to \a data.
//!
//! \exception std::out_of_range Thrown when offset is invalid.
//!
//! \todo fill pad bytes with random bytes
unsigned EncoreBootImage::LoadCommand::getDataBlocks(unsigned offset, unsigned maxCount, cipher_block_t * data)
{
          assert(data);
          assert(maxCount != 0);

          uint32_t blockCount = getDataBlockCount();

          // check offset
          if (offset >= blockCount)
          {
                    throw std::out_of_range("invalid offset");
          }

          // figure out how many blocks to return
          unsigned resultBlocks = blockCount - offset;
          if (resultBlocks > maxCount)
          {
                    resultBlocks = maxCount;

                    // exclude last block if there is padding
                    if (m_padCount && (offset != blockCount - 1) && (offset + resultBlocks == blockCount))
                    {
                              resultBlocks--;
                    }
          }

          // if there are pad bytes, handle the last block specially
          if (m_padCount && offset == blockCount - 1)
          {
                    // copy the remainder of the load data into the first part of the result block
                    unsigned remainderLength = sizeof(cipher_block_t) - m_padCount;
                    memcpy(data, &m_data[sizeof(cipher_block_t) * offset], remainderLength);

                    // copy pad bytes we previously generated into the last part of the result block
                    // data is a cipher block pointer, so indexing is done on cipher block
                    // boundaries, thus we need a byte pointer to index properly
                    uint8_t * bytePtr = reinterpret_cast<uint8_t*>(data);
                    memcpy(bytePtr + remainderLength, &m_padding, m_padCount);
          }
          else
          {
                    memcpy(data, &m_data[sizeof(cipher_block_t) * offset], sizeof(cipher_block_t) * resultBlocks);
          }

          return resultBlocks;
}

//! Fills #m_padding with random bytes that may be used to fill up the last data
//! cipher block.
void EncoreBootImage::LoadCommand::fillPadding()
{
          RandomNumberGenerator rng;
          rng.generateBlock(m_padding, sizeof(m_padding));
}

void EncoreBootImage::LoadCommand::debugPrint() const
{
          Log::log(Logger::INFO2, "  LOAD | adr=0x%08x | len=0x%08x | crc=0x%08x | flg=0x%08x\n", m_address, m_length, calculateCRC(), m_loadDCD ? ROM_LOAD_DCD : 0);
}

//! The pattern, address, and count are all initialized to zero, and the pattern
//! size is set to a word.
EncoreBootImage::FillCommand::FillCommand()
:         BootCommand(), m_address(0), m_count(0), m_pattern(0)
{
}

//! \param blocks Pointer to the raw data blocks.
//! \param count Number of blocks pointed to by \a blocks.
//! \param[out] consumed On exit, this points to the number of cipher blocks that were occupied
//!                 by the command. Should be at least 1 for every command. This must not be NULL
//!                 on entry!
//!
//! \exception std::runtime_error Thrown if header fields are invalid.
void EncoreBootImage::FillCommand::initFromData(const cipher_block_t * blocks, unsigned count, unsigned * consumed)
{
    // check static fields
          const boot_command_t model = { 0, ROM_FILL_CMD, 0, 0, 0, 0 };
          const boot_command_t * header = reinterpret_cast<const boot_command_t *>(blocks);
          validateHeader(&model, header, CMD_TAG_FIELD | CMD_FLAGS_FIELD);

    // read fields from header
          m_address = ENDIAN_LITTLE_TO_HOST_U32(header->m_address);
          m_count = ENDIAN_LITTLE_TO_HOST_U32(header->m_count);
    m_pattern = ENDIAN_LITTLE_TO_HOST_U32(header->m_data);

          *consumed = 1;
}

void EncoreBootImage::FillCommand::fillCommandHeader(boot_command_t & header)
{
          header.m_tag = getTag();
          header.m_flags = 0;
          header.m_address = ENDIAN_HOST_TO_LITTLE_U32(m_address);
          header.m_count = ENDIAN_HOST_TO_LITTLE_U32(m_count);
          header.m_data = ENDIAN_HOST_TO_LITTLE_U32(m_pattern);
          header.m_checksum = calculateChecksum(header);    // do this last
}

//! Extends the pattern across 32 bits.
//!
void EncoreBootImage::FillCommand::setPattern(uint8_t pattern)
{
          m_pattern = (pattern << 24) | (pattern << 16) | (pattern << 8) | pattern;
}

//! Extends the pattern across 32 bits.
//!
void EncoreBootImage::FillCommand::setPattern(uint16_t pattern)
{
          m_pattern = (pattern << 16) | pattern;
}

void EncoreBootImage::FillCommand::setPattern(uint32_t pattern)
{
          m_pattern = pattern;
}

void EncoreBootImage::FillCommand::debugPrint() const
{
          Log::log(Logger::INFO2, "  FILL | adr=0x%08x | len=0x%08x | ptn=0x%08x\n", m_address, m_count, m_pattern);
}

//! \param blocks Pointer to the raw data blocks.
//! \param count Number of blocks pointed to by \a blocks.
//! \param[out] consumed On exit, this points to the number of cipher blocks that were occupied
//!                 by the command. Should be at least 1 for every command. This must not be NULL
//!                 on entry!
//!
//! \exception std::runtime_error Thrown if header fields are invalid.
void EncoreBootImage::ModeCommand::initFromData(const cipher_block_t * blocks, unsigned count, unsigned * consumed)
{
    // check static fields
          const boot_command_t model = { 0, ROM_MODE_CMD, 0, 0, 0, 0 };
          const boot_command_t * header = reinterpret_cast<const boot_command_t *>(blocks);
          validateHeader(&model, header, CMD_TAG_FIELD | CMD_FLAGS_FIELD | CMD_ADDRESS_FIELD | CMD_COUNT_FIELD);

    // read fields from header
    m_mode = ENDIAN_LITTLE_TO_HOST_U32(header->m_data);

          *consumed = 1;
}

void EncoreBootImage::ModeCommand::fillCommandHeader(boot_command_t & header)
{
          header.m_tag = getTag();
          header.m_flags = 0;
          header.m_address = 0;
          header.m_count = 0;
          header.m_data = ENDIAN_HOST_TO_LITTLE_U32(m_mode);
          header.m_checksum = calculateChecksum(header);    // do this last
}

void EncoreBootImage::ModeCommand::debugPrint() const
{
          Log::log(Logger::INFO2, "  MODE | mod=0x%08x\n", m_mode);
}

//! \param blocks Pointer to the raw data blocks.
//! \param count Number of blocks pointed to by \a blocks.
//! \param[out] consumed On exit, this points to the number of cipher blocks that were occupied
//!                 by the command. Should be at least 1 for every command. This must not be NULL
//!                 on entry!
//!
//! \exception std::runtime_error Thrown if header fields are invalid.
void EncoreBootImage::JumpCommand::initFromData(const cipher_block_t * blocks, unsigned count, unsigned * consumed)
{
    // check static fields
          const boot_command_t model = { 0, getTag(), 0, 0, 0, 0 };
          const boot_command_t * header = reinterpret_cast<const boot_command_t *>(blocks);
          validateHeader(&model, header, CMD_TAG_FIELD | CMD_COUNT_FIELD);

    // read fields from header
    m_address = ENDIAN_LITTLE_TO_HOST_U32(header->m_address);
    m_argument = ENDIAN_LITTLE_TO_HOST_U32(header->m_data);
          m_isHAB = (ENDIAN_LITTLE_TO_HOST_U16(header->m_flags) & ROM_HAB_EXEC) != 0;

          *consumed = 1;
}

void EncoreBootImage::JumpCommand::fillCommandHeader(boot_command_t & header)
{
          header.m_tag = getTag();
          header.m_flags = ENDIAN_HOST_TO_LITTLE_U16(m_isHAB ? ROM_HAB_EXEC : 0);
          header.m_address = ENDIAN_HOST_TO_LITTLE_U32(m_address);
          header.m_count = 0;
          header.m_data = ENDIAN_HOST_TO_LITTLE_U32(m_argument);
          header.m_checksum = calculateChecksum(header);    // do this last
}

void EncoreBootImage::JumpCommand::debugPrint() const
{
          Log::log(Logger::INFO2, "  JUMP | adr=0x%08x | arg=0x%08x | flg=0x%08x\n", m_address, m_argument, m_isHAB ? ROM_HAB_EXEC : 0);
}

void EncoreBootImage::CallCommand::debugPrint() const
{
          Log::log(Logger::INFO2, "  CALL | adr=0x%08x | arg=0x%08x | flg=0x%08x\n", m_address, m_argument, m_isHAB ? ROM_HAB_EXEC : 0);
}

//! Only if the section has been assigned a boot image owner object will this
//! method be able to fill in the #section_header_t::m_offset field. If no
//! boot image has been set the offset will be set to 0.
void EncoreBootImage::Section::fillSectionHeader(section_header_t & header)
{
          header.m_tag = getIdentifier();
          header.m_offset = 0;
          header.m_length = ENDIAN_HOST_TO_LITTLE_U32(getBlockCount());
          header.m_flags = ENDIAN_HOST_TO_LITTLE_U32(getFlags());

          // if we're attached to an image, we can compute our real offset
          if (m_image)
          {
                    header.m_offset = ENDIAN_HOST_TO_LITTLE_U32(m_image->getSectionOffset(this));
          }
}

//! The alignment will never be less than 16, since that is the size of the
//! cipher block which is the basic unit of the boot image format. If an
//! alignment less than 16 is set it will be ignored.
//!
//! \param alignment Alignment in bytes for this section. Must be a power of two.
//!                 Ignored if less than 16.
void EncoreBootImage::Section::setAlignment(unsigned alignment)
{
          if (alignment > BOOT_IMAGE_MINIMUM_SECTION_ALIGNMENT)
          {
                    m_alignment = alignment;
          }
}

//! This method calculates the number of padding blocks that need to be inserted
//! from a given offset for the section to be properly aligned. The value returned
//! is the number of padding blocks that should be inserted starting just after
//! \a offset to align the first cipher block of the section contents. The section's
//! boot tag is \i not taken into account by this method, so the caller must
//! deal with that herself.
//!
//! \param offset Start offset in cipher blocks (not bytes).
//!
//! \return A number of cipher blocks of padding to insert.
unsigned EncoreBootImage::Section::getPadBlockCountForOffset(unsigned offset)
{
          // convert alignment from byte to block alignment
          unsigned blockAlignment = m_alignment >> 4;

          unsigned nextAlignmentOffset = (offset + blockAlignment - 1) / blockAlignment * blockAlignment;

          return nextAlignmentOffset - offset;
}

EncoreBootImage::BootSection::~BootSection()
{
          deleteCommands();
}

void EncoreBootImage::BootSection::deleteCommands()
{
          // dispose of all sections
          iterator_t it = begin();
          for (; it != end(); ++it)
          {
                    delete *it;
          }
}

//! Always returns at least 1 for the required tag command.
//!
unsigned EncoreBootImage::BootSection::getBlockCount() const
{
          unsigned count = 0;

          const_iterator_t it = begin();
          for (; it != end(); ++it)
          {
                    count += (*it)->getBlockCount();
          }

          return count;
}

//! Up to \a maxCount cipher blocks are copied into the buffer pointed to by
//! the \a data argument. A return value of 0 indicates that
//! no more blocks are available. The index of the first block to copy is
//! held in the \a offset argument.
//!
//! \param offset Starting block number to copy. Zero means the first available block.
//! \param maxCount Up to this number of blocks may be copied into \a data.
//! \param data Buffer for outgoing cipher blocks. Must have enough room to hold
//!                 \a maxCount blocks.
//!
//! \return The number of cipher blocks copied into \a data.
//! \retval 0 No more blocks are available and nothing was written to \a data.
unsigned EncoreBootImage::BootSection::getBlocks(unsigned offset, unsigned maxCount, cipher_block_t * data)
{
          assert(data);
          assert(maxCount >= 1);

          unsigned currentOffset = 0;
          unsigned readCount = maxCount;

          iterator_t it = begin();
          for (; it != end(); ++it)
          {
                    BootCommand * command = *it;
                    unsigned commandBlocks = command->getBlockCount();

                    // this should never be false!
                    assert(offset >= currentOffset);

                    // skip forward until we hit the requested offset
                    if (offset >= currentOffset + commandBlocks)
                    {
                              currentOffset += commandBlocks;
                              continue;
                    }

                    // read from this command
                    unsigned commandOffset = offset - currentOffset;
                    unsigned commandRemaining = commandBlocks - commandOffset;
                    if (readCount > commandRemaining)
                    {
                              readCount = commandRemaining;
                    }
                    return command->getBlocks(commandOffset, readCount, data);
          }

          return 0;
}

//! The entire contents of the section must be in memory, pointed to by \a blocks.
//! Any commands that had previously been added to the section are disposed of.
//!
//! \param blocks Pointer to the section contents.
//! \param count Number of blocks pointed to by \a blocks.
//!
//! \exception std::runtime_error Thrown if a boot command cannot be created from
//!                 the cipher block stream.
void EncoreBootImage::BootSection::fillFromData(const cipher_block_t * blocks, unsigned count)
{
          // start with an empty slate
          deleteCommands();

          const cipher_block_t * currentBlock = blocks;
          unsigned remaining = count;
          while (remaining)
          {
                    // try to create a command from the next cipher block. the number of
                    // blocks the command used up is returned in consumed.
                    unsigned consumed;
                    BootCommand * command = BootCommand::createFromData(currentBlock, remaining, &consumed);
                    if (!command)
                    {
                              throw std::runtime_error("invalid boot section data");
                    }

                    addCommand(command);

                    // update loop counters
                    remaining -= consumed;
                    currentBlock += consumed;
          }
}

void EncoreBootImage::BootSection::debugPrint() const
{
          Log::log(Logger::INFO2, "Boot Section 0x%08x:\n", m_identifier);

          const_iterator_t it = begin();
          for (; it != end(); ++it)
          {
                    const BootCommand * command = *it;
                    command->debugPrint();
          }
}

//! A copy is made of \a data. Any previously assigned data is disposed of.
//!
void EncoreBootImage::DataSection::setData(const uint8_t * data, unsigned length)
{
          m_data = new uint8_t[length];
          memcpy(m_data.get(), data, length);
          m_length = length;
}

//! The section takes ownership of \a data and will dispose of it using the
//! array delete operator upon its destruction.
void EncoreBootImage::DataSection::setDataNoCopy(const uint8_t * data, unsigned length)
{
          m_data = data;
          m_length = length;
}

unsigned EncoreBootImage::DataSection::getBlockCount() const
{
          return numberOfCipherBlocks(m_length);
}

unsigned EncoreBootImage::DataSection::getBlocks(unsigned offset, unsigned maxCount, cipher_block_t * data)
{
          assert(data);
          assert(maxCount != 0);

          unsigned blockCount = getBlockCount();
          unsigned padCount = sizeOfPaddingForCipherBlocks(m_length);

          // check offset
          if (offset >= blockCount)
          {
                    throw std::out_of_range("invalid offset");
          }

          // figure out how many blocks to return
          unsigned resultBlocks = blockCount - offset;
          if (resultBlocks > maxCount)
          {
                    resultBlocks = maxCount;

                    // exclude last block if there is padding
                    if (padCount && (offset != blockCount - 1) && (offset + resultBlocks == blockCount))
                    {
                              resultBlocks--;
                    }
          }

          // if there are pad bytes, handle the last block specially
          if (padCount && offset == blockCount - 1)
          {
                    // copy the remainder of the load data into the first part of the result block
                    unsigned remainderLength = sizeof(cipher_block_t) - padCount;
                    memcpy(data, &m_data[sizeOfCipherBlocks(offset)], remainderLength);

                    // set pad bytes to zeroes.
                    // data is a cipher block pointer, so indexing is done on cipher block
                    // boundaries, thus we need a byte pointer to index properly
                    uint8_t * bytePtr = reinterpret_cast<uint8_t*>(data);
                    memset(bytePtr + remainderLength, 0, padCount);
          }
          else
          {
                    memcpy(data, &m_data[sizeOfCipherBlocks(offset)], sizeOfCipherBlocks(resultBlocks));
          }

          return resultBlocks;
}

void EncoreBootImage::DataSection::debugPrint() const
{
          Log::log(Logger::INFO2, "Data Section 0x%08x: (%d bytes, %d blocks)\n", m_identifier, m_length, getBlockCount());
}