PEM_READ(3)

NAME
PEM_write, PEM_write_bio, PEM_read, PEM_read_bio, PEM_do_header, PEM_get_EVP_CIPHER_INFO - PEM encoding routines

SYNOPSIS
#include <openssl/pem.h>
int
PEM_write(FILE *fp, char *name, char *header, unsigned char *data, long len);
int
PEM_write_bio(BIO *bp, const char *name, char *header, unsigned char *data, long len);
int
PEM_read(FILE *fp, char **name, char **header, unsigned char **data, long *len);
int
PEM_read_bio(BIO *bp, char **name, char **header, unsigned char **data, long *len);
int
PEM_get_EVP_CIPHER_INFO(char *header, EVP_CIPHER_INFO *cinfo);
int
PEM_do_header(EVP_CIPHER_INFO *cinfo, unsigned char *data, long *len, pem_password_cb *cb, void *u);

DESCRIPTION
These functions read and write PEM-encoded objects, using the PEM type name, any additional header information, and the raw data of length len.

PEM is the binary content encoding first defined in IETF RFC 1421. The content is a series of base64-encoded lines, surrounded by begin/end markers each on their own line. For example:

    -----BEGIN PRIVATE KEY-----
    MIICdg....
    ... bhTQ==
    -----END PRIVATE KEY-----

Optional header line(s) may appear after the begin line, and their existence depends on the type of object being written or read.

PEM_write() writes to the file fp, while PEM_write_bio() writes to the BIO bp. The name is the name to use in the marker, the header is the header value or NULL, and data and len specify the data and its length.

The final data buffer is typically an ASN.1 object which can be decoded with the d2i_*() function appropriate to the type name; see d2i_X509(3) for examples.

PEM_read() reads from the file fp, while PEM_read_bio() reads from the BIO bp. Both skip any non-PEM data that precedes the start of the next PEM object. When an object is successfully retrieved, the type name from the "----BEGIN <type>-----" is returned via the name argument, any encapsulation headers are returned in header, and the base64-decoded content and its length are returned via data and len, respectively. The name, header, and data pointers should be freed by the caller when no longer needed.

The remaining functions are deprecated because the underlying PEM encryption format is obsolete and should be avoided. It uses an encryption format with an OpenSSL-specific key-derivation function, which employs MD5 with an iteration count of 1. Instead, private keys should be stored in PKCS#8 form, with a strong PKCS#5 v2.0 PBE; see PEM_write_PrivateKey(3) and d2i_PKCS8PrivateKey_bio(3).

PEM_get_EVP_CIPHER_INFO() can be used to determine the data returned by PEM_read() or PEM_read_bio() is encrypted and to retrieve the associated cipher and IV. The caller passes a pointer to a structure of type EVP_CIPHER_INFO via the cinfo argument and the header returned via PEM_read() or PEM_read_bio(). If the call is successful, 1 is returned and the cipher and IV are stored at the address pointed to by cinfo. When the header is malformed or not supported or when the cipher is unknown or some internal error happens, 0 is returned.

PEM_do_header() can then be used to decrypt the data if the header indicates encryption. The cinfo argument is a pointer to the structure initialized by the previous call to PEM_get_EVP_CIPHER_INFO(). The data and len arguments are those returned by the previous call to PEM_read() or PEM_read_bio(). The cb and u arguments make it possible to override the default password prompt function as described in PEM_read_PrivateKey(3). On successful completion, the data is decrypted in place, and len is updated to indicate the plaintext length.

If the data is a priori known to not be encrypted, then neither PEM_do_header() nor PEM_get_EVP_CIPHER_INFO() need to be called.

RETURN VALUES
PEM_read() and PEM_read_bio() return 1 on success or 0 on failure. The latter includes the case when no more PEM objects remain in the input file. To distinguish end of file from more serious errors, the caller must peek at the error stack and check for PEM_R_NO_START_LINE, which indicates that no more PEM objects were found. See ERR_peek_last_error(3) and ERR_GET_REASON(3).

PEM_get_EVP_CIPHER_INFO() and PEM_do_header() return 1 on success or 0 on failure. The data is likely meaningless if these functions fail.

SEE ALSO
d2i_PKCS8PrivateKey_bio(3), ERR_GET_LIB(3), ERR_peek_last_error(3), PEM_bytes_read_bio(3), PEM_read_bio_PrivateKey(3)