=pod

=head1 NAME

PEM_read, PEM_read_bio, PEM_do_header, PEM_get_EVP_CIPHER_INFO, PEM_write,
PEM_write_bio, PEM_ASN1_write, PEM_ASN1_write_bio, PEM_ASN1_write_bio_ctx
- PEM encoding routines

=head1 SYNOPSIS

 #include <openssl/pem.h>

 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);

 int PEM_write(FILE *fp, const char *name, const char *header,
               const unsigned char *data, long len);
 int PEM_write_bio(BIO *bp, const char *name, const char *header,
                   const unsigned char *data, long len);
 int PEM_ASN1_write(i2d_of_void *i2d, const char *name, FILE *fp,
                    const void *x, const EVP_CIPHER *enc,
                    const unsigned char *kstr, int klen,
                    pem_password_cb *callback, void *u);
 int PEM_ASN1_write_bio(i2d_of_void *i2d, const char *name, BIO *bp,
                        const void *x, const EVP_CIPHER *enc,
                        const unsigned char *kstr, int klen,
                        pem_password_cb *callback, void *u);
 int PEM_ASN1_write_bio_ctx(OSSL_i2d_of_void_ctx *i2d, void *vctx,
                            const char *name, BIO *bp, const void *x,
                            const EVP_CIPHER *enc, const unsigned char *kstr,
                            int klen, pem_password_cb *callback, void *u);

=head1 DESCRIPTION

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

PEM is the term used for 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 B<fp>, while PEM_write_bio() writes to
the BIO B<bp>.  The B<name> is the name to use in the marker, the
B<header> is the header value or NULL, and B<data> and B<len> specify
the data and its length.

The final B<data> buffer is typically an ASN.1 object which can be decoded with
the B<d2i> function appropriate to the type B<name>; see L<d2i_X509(3)>
for examples.

PEM_read() reads from the file B<fp>, while PEM_read_bio() reads
from the BIO B<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 B<name> argument, any encapsulation headers
are returned in B<header> and the base64-decoded content and its length are
returned via B<data> and B<len> respectively.
The B<name>, B<header> and B<data> pointers are allocated via OPENSSL_malloc()
and should be freed by the caller via OPENSSL_free() when no longer needed.

PEM_get_EVP_CIPHER_INFO() can be used to determine the B<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 structure of type B<EVP_CIPHER_INFO> via the
B<cinfo> argument and the B<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 B<cinfo>.
When the header is malformed, or not supported or when the cipher is unknown
or some internal error happens 0 is returned.
This function is deprecated, see B<NOTES> below.

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

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

=head1 RETURN VALUES

PEM_read(), and PEM_read_bio() return 1 on success and 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 B<PEM_R_NO_START_LINE>, which indicates that no more
PEM objects were found.  See L<ERR_peek_last_error(3)>, L<ERR_GET_REASON(3)>.

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

=head1 NOTES

The PEM_get_EVP_CIPHER_INFO() and PEM_do_header() functions are deprecated.
This is 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 L<PEM_write_PrivateKey(3)> and L<d2i_PKCS8PrivateKey_bio(3)>.

PEM_do_header() makes no assumption regarding the pass phrase received from the
password callback.
It will simply be treated as a byte sequence.

PEM_write() and PEM_write_bio() return the number of encoded bytes (not
counting the PEM header and end marker) written on success or 0 on failure.

PEM_ASN1_write_bio(), and PEM_ASN1_write_bio_ctx() return 1 on success and 0 on
failure.  The latter function passes an additional application-provided context
value to the B<i2d> function that serialises the input ASN.1 object.

=head1 SEE ALSO

L<ERR_peek_last_error(3)>, L<ERR_GET_LIB(3)>,
L<d2i_PKCS8PrivateKey_bio(3)>,
L<passphrase-encoding(7)>

=head1 HISTORY

The PEM_ASN1_write_bio_ctx() function was added in OpenSSL 3.5.

=head1 COPYRIGHT

Copyright 1998-2025 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file LICENSE in the source distribution or at
L<https://www.openssl.org/source/license.html>.

=cut
