12ce9ea25d
Partially document the ASN1 template stuff, and its use for i2d/d2i and PEM I/O. Reviewed-by: Richard Levitte <levitte@openssl.org>
130 lines
5.2 KiB
Text
130 lines
5.2 KiB
Text
=pod
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=head1 NAME
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PEM_write, PEM_write_bio,
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PEM_read, PEM_read_bio, PEM_do_header, PEM_get_EVP_CIPHER_INFO,
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pem_password_cb
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- PEM encoding routines
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=head1 SYNOPSIS
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#include <openssl/pem.h>
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int PEM_write(FILE *fp, const char *name, const char *header,
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const unsigned char *data, long len)
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int PEM_write_bio(BIO *bp, const char *name, const char *header,
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const unsigned char *data, long len)
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int PEM_read(FILE *fp, char **name, char **header,
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unsigned char **data, long *len);
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int PEM_read_bio(BIO *bp, char **name, char **header,
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unsigned char **data, long *len);
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int PEM_get_EVP_CIPHER_INFO(char *header, EVP_CIPHER_INFO *cinfo);
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int PEM_do_header(EVP_CIPHER_INFO *cinfo, unsigned char *data, long *len,
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pem_password_cb *cb, void *u);
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typedef int pem_password_cb (char *buf, int size, int rwflag, void *u);
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=head1 DESCRIPTION
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These functions read and write PEM-encoded objects, using the PEM
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type B<name>, any additional B<header> information, and the raw
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B<data> of length B<len>.
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PEM is the term used for binary content encoding first defined in IETF
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RFC 1421. The content is a series of base64-encoded lines, surrounded
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by begin/end markers each on their own line. For example:
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-----BEGIN PRIVATE KEY-----
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MIICdg....
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... bhTQ==
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-----END PRIVATE KEY-----
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Optional header line(s) may appear after the begin line, and their
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existence depends on the type of object being written or read.
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PEM_write() writes to the file B<fp>, while PEM_write_bio() writes to
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the BIO B<bp>. The B<name> is the name to use in the marker, the
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B<header> is the header value or NULL, and B<data> and B<len> specify
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the data and its length.
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The final B<data> buffer is typically an ASN.1 object which can be decoded with
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the B<d2i> function appropriate to the type B<name>; see L<d2i_X509(3)>
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for examples.
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PEM_read() reads from the file B<fp>, while PEM_read_bio() reads
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from the BIO B<bp>.
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Both skip any non-PEM data that precedes the start of the next PEM object.
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When an object is successfuly retrieved, the type name from the "----BEGIN
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<type>-----" is returned via the B<name> argument, any encapsulation headers
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are returned in B<header> and the base64-decoded content and its length are
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returned via B<data> and B<len> respectively.
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The B<name>, B<header> and B<data> pointers are allocated via OPENSSL_malloc()
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and should be freed by the caller via OPENSSL_free() when no longer needed.
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PEM_get_EVP_CIPHER_INFO() can be used to determine the B<data> returned by
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PEM_read() or PEM_read_bio() is encrypted and to retrieve the associated cipher
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and IV.
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The caller passes a pointer to structure of type B<EVP_CIPHER_INFO> via the
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B<cinfo> argument and the B<header> returned via PEM_read() or PEM_read_bio().
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If the call is succesful 1 is retured and the cipher and IV are stored at the
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address pointed to by B<cinfo>.
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When the header is malformed, or not supported or when the cipher is unknown
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or some internal error happens 0 is returned.
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This function is deprecated, see B<NOTES> below.
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PEM_do_header() can then be used to decrypt the data if the header
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indicates encryption.
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The B<cinfo> argument is a pointer to the structure initialized by the previous
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call to PEM_get_EVP_CIPHER_INFO().
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The B<data> and B<len> arguments are those returned by the previous call to
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PEM_read() or PEM_read_bio().
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The B<cb> and B<u> arguments make it possible to override the default password
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prompt function as described in L<PEM_read_PrivateKey(3)>.
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On successful completion the B<data> is decrypted in place, and B<len> is
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updated to indicate the plaintext length.
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This function is deprecated, see B<NOTES> below.
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If the data is a priori known to not be encrypted, then neither PEM_do_header()
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nor PEM_get_EVP_CIPHER_INFO() need be called.
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=head1 RETURN VALUES
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PEM_read() and PEM_read_bio() return 1 on success and 0 on failure, the latter
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includes the case when no more PEM objects remain in the input file.
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To distinguish end of file from more serious errors the caller must peek at the
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error stack and check for B<PEM_R_NO_START_LINE>, which indicates that no more
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PEM objects were found. See L<ERR_peek_last_error(3)>, L<ERR_GET_REASON(3)>.
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PEM_get_EVP_CIPHER_INFO() and PEM_do_header() return 1 on success, and 0 on
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failure.
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The B<data> is likely meaningless if these functions fail.
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=head1 NOTES
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The PEM_get_EVP_CIPHER_INFO() and PEM_do_header() functions are deprecated.
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This is because the underlying PEM encryption format is obsolete, and should
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be avoided.
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It uses an encryption format with an OpenSSL-specific key-derivation function,
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which employs MD5 with an iteration count of 1!
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Instead, private keys should be stored in PKCS#8 form, with a strong PKCS#5
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v2.0 PBE.
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See L<PEM_write_PrivateKey(3)> and L<d2i_PKCS8PrivateKey_bio(3)>.
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=head1 SEE ALSO
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L<ERR_peek_last_error(3)>, L<ERR_GET_LIB(3)>,
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L<d2i_PKCS8PrivateKey_bio(3)>.
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=head1 COPYRIGHT
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Copyright 1998-2016 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the OpenSSL license (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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