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✏️ Editing: PEM_do_header.3

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.\" ========================================================================
.\"
.IX Title "PEM_READ 3"
.TH PEM_READ 3 "2023-09-11" "1.1.1w" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
PEM_write, PEM_write_bio, PEM_read, PEM_read_bio, PEM_do_header, PEM_get_EVP_CIPHER_INFO \&\- PEM encoding routines
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/pem.h>
\&
\& 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_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);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
These functions read and write PEM-encoded objects, using the \s-1PEM\s0
type \fBname\fR, any additional \fBheader\fR information, and the raw
\&\fBdata\fR of length \fBlen\fR.
.PP
\&\s-1PEM\s0 is the term used for binary content encoding first defined in \s-1IETF
RFC 1421.\s0  The content is a series of base64\-encoded lines, surrounded
by begin/end markers each on their own line.  For example:
.PP
.Vb 4
\& \-\-\-\-\-BEGIN PRIVATE KEY\-\-\-\-\-
\& MIICdg....
\& ... bhTQ==
\& \-\-\-\-\-END PRIVATE KEY\-\-\-\-\-
.Ve
.PP
Optional header line(s) may appear after the begin line, and their
existence depends on the type of object being written or read.
.PP
\&\fBPEM_write()\fR writes to the file \fBfp\fR, while \fBPEM_write_bio()\fR writes to
the \s-1BIO\s0 \fBbp\fR.  The \fBname\fR is the name to use in the marker, the
\&\fBheader\fR is the header value or \s-1NULL,\s0 and \fBdata\fR and \fBlen\fR specify
the data and its length.
.PP
The final \fBdata\fR buffer is typically an \s-1ASN.1\s0 object which can be decoded with
the \fBd2i\fR function appropriate to the type \fBname\fR; see \fBd2i_X509\fR\|(3)
for examples.
.PP
\&\fBPEM_read()\fR reads from the file \fBfp\fR, while \fBPEM_read_bio()\fR reads
from the \s-1BIO\s0 \fBbp\fR.
Both skip any non-PEM data that precedes the start of the next \s-1PEM\s0 object.
When an object is successfully retrieved, the type name from the \*(L"\-\-\-\-BEGIN
<type>\-\-\-\-\-\*(R" is returned via the \fBname\fR argument, any encapsulation headers
are returned in \fBheader\fR and the base64\-decoded content and its length are
returned via \fBdata\fR and \fBlen\fR respectively.
The \fBname\fR, \fBheader\fR and \fBdata\fR pointers are allocated via \fBOPENSSL_malloc()\fR
and should be freed by the caller via \fBOPENSSL_free()\fR when no longer needed.
.PP
\&\fBPEM_get_EVP_CIPHER_INFO()\fR can be used to determine the \fBdata\fR returned by
\&\fBPEM_read()\fR or \fBPEM_read_bio()\fR is encrypted and to retrieve the associated cipher
and \s-1IV.\s0
The caller passes a pointer to structure of type \fB\s-1EVP_CIPHER_INFO\s0\fR via the
\&\fBcinfo\fR argument and the \fBheader\fR returned via \fBPEM_read()\fR or \fBPEM_read_bio()\fR.
If the call is successful 1 is returned and the cipher and \s-1IV\s0 are stored at the
address pointed to by \fBcinfo\fR.
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 \fB\s-1NOTES\s0\fR below.
.PP
\&\fBPEM_do_header()\fR can then be used to decrypt the data if the header
indicates encryption.
The \fBcinfo\fR argument is a pointer to the structure initialized by the previous
call to \fBPEM_get_EVP_CIPHER_INFO()\fR.
The \fBdata\fR and \fBlen\fR arguments are those returned by the previous call to
\&\fBPEM_read()\fR or \fBPEM_read_bio()\fR.
The \fBcb\fR and \fBu\fR arguments make it possible to override the default password
prompt function as described in \fBPEM_read_PrivateKey\fR\|(3).
On successful completion the \fBdata\fR is decrypted in place, and \fBlen\fR is
updated to indicate the plaintext length.
This function is deprecated, see \fB\s-1NOTES\s0\fR below.
.PP
If the data is a priori known to not be encrypted, then neither \fBPEM_do_header()\fR
nor \fBPEM_get_EVP_CIPHER_INFO()\fR need be called.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fBPEM_read()\fR and \fBPEM_read_bio()\fR return 1 on success and 0 on failure, the latter
includes the case when no more \s-1PEM\s0 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 \fB\s-1PEM_R_NO_START_LINE\s0\fR, which indicates that no more
\&\s-1PEM\s0 objects were found.  See \fBERR_peek_last_error\fR\|(3), \s-1\fBERR_GET_REASON\s0\fR\|(3).
.PP
\&\fBPEM_get_EVP_CIPHER_INFO()\fR and \fBPEM_do_header()\fR return 1 on success, and 0 on
failure.
The \fBdata\fR is likely meaningless if these functions fail.
.SH "NOTES"
.IX Header "NOTES"
The \fBPEM_get_EVP_CIPHER_INFO()\fR and \fBPEM_do_header()\fR functions are deprecated.
This is because the underlying \s-1PEM\s0 encryption format is obsolete, and should
be avoided.
It uses an encryption format with an OpenSSL-specific key-derivation function,
which employs \s-1MD5\s0 with an iteration count of 1!
Instead, private keys should be stored in PKCS#8 form, with a strong PKCS#5
v2.0 \s-1PBE.\s0
See \fBPEM_write_PrivateKey\fR\|(3) and \fBd2i_PKCS8PrivateKey_bio\fR\|(3).
.PP
\&\fBPEM_do_header()\fR makes no assumption regarding the pass phrase received from the
password callback.
It will simply be treated as a byte sequence.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBERR_peek_last_error\fR\|(3), \s-1\fBERR_GET_LIB\s0\fR\|(3),
\&\fBd2i_PKCS8PrivateKey_bio\fR\|(3),
\&\fBpassphrase\-encoding\fR\|(7)
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 1998\-2018 The OpenSSL Project Authors. All Rights Reserved.
.PP
Licensed under the OpenSSL license (the \*(L"License\*(R").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file \s-1LICENSE\s0 in the source distribution or at
<https://www.openssl.org/source/license.html>.

MR SKB