EVP_PKEY_SIGN(3ossl) OpenSSL EVP_PKEY_SIGN(3ossl)
NAME
EVP_PKEY_sign_init, EVP_PKEY_sign_init_ex, EVP_PKEY_sign_init_ex2,
EVP_PKEY_sign, EVP_PKEY_sign_message_init,
EVP_PKEY_sign_message_update, EVP_PKEY_sign_message_final - sign using
a public key algorithm
SYNOPSIS
#include <openssl/evp.h>
int EVP_PKEY_sign_init(EVP_PKEY_CTX *ctx);
int EVP_PKEY_sign_init_ex(EVP_PKEY_CTX *ctx, const OSSL_PARAM params[]);
int EVP_PKEY_sign_init_ex2(EVP_PKEY_CTX *ctx, EVP_SIGNATURE *algo,
const OSSL_PARAM params[]);
int EVP_PKEY_sign_message_init(EVP_PKEY_CTX *ctx, EVP_SIGNATURE *algo,
const OSSL_PARAM params[]);
int EVP_PKEY_sign_message_update(EVP_PKEY_CTX *ctx,
unsigned char *in, size_t inlen);
int EVP_PKEY_sign_message_final(EVP_PKEY_CTX *ctx, unsigned char *sig,
size_t *siglen, size_t sigsize);
int EVP_PKEY_sign(EVP_PKEY_CTX *ctx,
unsigned char *sig, size_t *siglen,
const unsigned char *tbs, size_t tbslen);
DESCRIPTION
EVP_PKEY_sign_init() initializes a public key algorithm context ctx for
signing using the algorithm given when the context was created using
EVP_PKEY_CTX_new(3) or variants thereof. The algorithm is used to
fetch a EVP_SIGNATURE method implicitly, see "Implicit fetch" in
provider(7) for more information about implicit fetches.
EVP_PKEY_sign_init_ex() is the same as EVP_PKEY_sign_init() but
additionally sets the passed parameters params on the context before
returning.
EVP_PKEY_sign_init_ex2() initializes a public key algorithm context ctx
for signing a pre-computed message digest using the algorithm given by
algo and the key given through EVP_PKEY_CTX_new(3) or
EVP_PKEY_CTX_new_from_pkey(3). A context ctx without a pre-loaded key
cannot be used with this function. This function provides almost the
same functionality as EVP_PKEY_sign_init_ex(), but is uniquely intended
to be used with a pre-computed messsage digest, and allows pre-
determining the exact conditions for that message digest, if a
composite signature algorithm (such as RSA-SHA256) was fetched.
Following a call to this function, setting parameters that modifies the
digest implementation or padding is not normally supported.
EVP_PKEY_sign_message_init() initializes a public key algorithm context
ctx for signing an unlimited size message using the algorithm given by
algo and the key given through EVP_PKEY_CTX_new(3) or
EVP_PKEY_CTX_new_from_pkey(3). Passing the message is supported both
in a one-shot fashion using EVP_PKEY_sign(3), and through the
combination of EVP_PKEY_sign_message_update() and
EVP_PKEY_sign_message_final(). This function enables using algorithms
that can process input of arbitrary length, such as ED25519, RSA-SHA256
and similar.
EVP_PKEY_sign_message_update() adds inlen bytes from in to the data to
be processed for signature. The signature algorithm specification and
implementation determine how the input bytes are processed and if
there's a limit on the total size of the input. See "NOTES" below for
a deeper explanation.
EVP_PKEY_sign_message_final() signs the processed data and places the
data in sig, and the number of signature bytes in *siglen, if the
number of bytes doesn't surpass the size given by sigsize. sig may be
NULL, and in that case, only *siglen is updated with the number of
signature bytes.
EVP_PKEY_sign(3) is a one-shot function that can be used with all the
init functions above. When initialization was done with
EVP_PKEY_sign_init(), EVP_PKEY_sign_init_ex() or
EVP_PKEY_sign_init_ex2(), the data specified by tbs and tbslen is
signed after appropriate padding. When initialization was done with
EVP_PKEY_sign_message_init(), the data specified by tbs and tbslen is
digested by the implied message digest algorithm, and the result is
signed after appropriate padding. If sig is NULL then the maximum size
of the output buffer is written to the siglen parameter. If sig is not
NULL, then before the call the siglen parameter should contain the
length of the sig buffer, and if the call is successful the signature
is written to sig and the amount of data written to siglen.
NOTES
General
Some signature implementations only accumulate the input data and do no
further processing before signing it (they expect the input to be a
digest), while others compress the data, typically by internally
producing a digest, and signing the result. Some of them support both
modes of operation at the same time. The caller is expected to know
how the chosen algorithm is supposed to behave and under what
conditions.
For example, an RSA implementation can be expected to only expect a
message digest as input, while ED25519 can be expected to process the
input with a hash, i.e. to produce the message digest internally, and
while RSA-SHA256 can be expected to handle either mode of operation,
depending on if the operation was initialized with
EVP_PKEY_sign_init_ex2() or with EVP_PKEY_sign_message_init().
Similarly, an RSA implementation usually expects additional details to
be set, like the message digest algorithm that the input is supposed to
be digested with, as well as the padding mode (see
EVP_PKEY_CTX_set_signature_md(3) and EVP_PKEY_CTX_set_rsa_padding(3)
and similar others), while an RSA-SHA256 implementation usually has
these details pre-set and immutable.
The functions described here can't be used to combine separate
algorithms. In particular, neither EVP_PKEY_CTX_set_signature_md(3)
nor the OSSL_PARAM parameter "digest" (OSSL_SIGNATURE_PARAM_DIGEST) can
be used to combine a signature algorithm with a hash algorithm to
process the input. In other words, it's not possible to specify a ctx
pre-loaded with an RSA pkey, or an algo that fetched "RSA" and try to
specify SHA256 separately to get the functionality of RSA-SHA256. If
combining algorithms in that manner is desired, please use
EVP_DigestSignInit(3) and associated functions.
Performing multiple signatures
When initialized using EVP_PKEY_sign_init_ex() or
EVP_PKEY_sign(3) can be called more than once
on the same context to have several one-shot operations performed using
the same parameters.
When initialized using EVP_PKEY_sign_message_init(), it's not possible
to call EVP_PKEY_sign(3) multiple times.
RETURN VALUES
All functions return 1 for success and 0 or a negative value for
failure.
In particular, EVP_PKEY_sign_init() and its other variants may return
-2 to indicate that the operation is not supported by the public key
algorithm.
EXAMPLES
RSA with PKCS#1 padding for SHA256
Sign data using RSA with PKCS#1 padding and a SHA256 digest as input:
#include <openssl/evp.h>
#include <openssl/rsa.h>
EVP_PKEY_CTX *ctx;
/* md is a SHA-256 digest in this example. */
unsigned char *md, *sig;
size_t mdlen = 32, siglen;
EVP_PKEY *signing_key;
/*
* NB: assumes signing_key and md are set up before the next
* step. signing_key must be an RSA private key and md must
* point to the SHA-256 digest to be signed.
*/
ctx = EVP_PKEY_CTX_new(signing_key, NULL /* no engine */);
if (ctx == NULL)
/* Error occurred */
if (EVP_PKEY_sign_init(ctx) <= 0)
/* Error */
if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) <= 0)
/* Error */
if (EVP_PKEY_CTX_set_signature_md(ctx, EVP_sha256()) <= 0)
/* Error */
/* Determine buffer length */
if (EVP_PKEY_sign(ctx, NULL, &siglen, md, mdlen) <= 0)
/* Error */
sig = OPENSSL_malloc(siglen);
if (sig == NULL)
/* malloc failure */
if (EVP_PKEY_sign(ctx, sig, &siglen, md, mdlen) <= 0)
/* Error */
/* Signature is siglen bytes written to buffer sig */
RSA-SHA256 with a pre-computed digest
Sign a digest with RSA-SHA256 using one-shot functions. To be noted is
that RSA-SHA256 is assumed to be an implementation of
"sha256WithRSAEncryption", for which the padding is pre-determined to
be RSA_PKCS1_PADDING, and the input digest is assumed to have been
computed using SHA256.
#include <openssl/evp.h>
#include <openssl/rsa.h>
EVP_PKEY_CTX *ctx;
/* md is a SHA-256 digest in this example. */
unsigned char *md, *sig;
size_t mdlen = 32, siglen;
EVP_PKEY *signing_key;
/*
* NB: assumes signing_key and md are set up before the next
* step. signing_key must be an RSA private key and md must
* point to the SHA-256 digest to be signed.
*/
ctx = EVP_PKEY_CTX_new(signing_key, NULL /* no engine */);
alg = EVP_SIGNATURE_fetch(NULL, "RSA-SHA256", NULL);
if (ctx == NULL)
/* Error occurred */
if (EVP_PKEY_sign_init_ex2(ctx, alg, NULL) <= 0)
/* Error */
/* Determine buffer length */
if (EVP_PKEY_sign(ctx, NULL, &siglen, md, mdlen) <= 0)
/* Error */
sig = OPENSSL_malloc(siglen);
if (sig == NULL)
/* malloc failure */
if (EVP_PKEY_sign(ctx, sig, &siglen, md, mdlen) <= 0)
/* Error */
/* Signature is siglen bytes written to buffer sig */
RSA-SHA256, one-shot
Sign a document with RSA-SHA256 using one-shot functions. To be noted
is that RSA-SHA256 is assumed to be an implementation of
"sha256WithRSAEncryption", for which the padding is pre-determined to
be RSA_PKCS1_PADDING.
#include <openssl/evp.h>
#include <openssl/rsa.h>
EVP_PKEY_CTX *ctx;
/* in is the input in this example. */
unsigned char *in, *sig;
/* inlen is the length of the input in this example. */
size_t inlen, siglen;
EVP_PKEY *signing_key;
EVP_SIGNATURE *alg;
/*
* NB: assumes signing_key, in and inlen are set up before
* the next step. signing_key must be an RSA private key,
* in must point to data to be digested and signed, and
* inlen must be the size of the data in bytes.
*/
ctx = EVP_PKEY_CTX_new(signing_key, NULL /* no engine */);
alg = EVP_SIGNATURE_fetch(NULL, "RSA-SHA256", NULL);
if (ctx == NULL || alg == NULL)
/* Error occurred */
if (EVP_PKEY_sign_message_init(ctx, alg, NULL) <= 0)
/* Error */
/* Determine sig buffer length */
if (EVP_PKEY_sign(ctx, NULL, &siglen, in, inlen) <= 0)
/* Error */
sig = OPENSSL_malloc(siglen);
if (sig == NULL)
/* malloc failure */
if (EVP_PKEY_sign(ctx, sig, &siglen, in, inlen) <= 0)
/* Error */
/* Signature is siglen bytes written to buffer sig */
RSA-SHA256, using update and final
This is the same as the previous example, but allowing stream-like
functionality.
#include <openssl/evp.h>
#include <openssl/rsa.h>
EVP_PKEY_CTX *ctx;
/* in is the input in this example. */
unsigned char *in, *sig;
/* inlen is the length of the input in this example. */
size_t inlen, siglen;
EVP_PKEY *signing_key;
EVP_SIGNATURE *alg;
/*
* NB: assumes signing_key, in and inlen are set up before
* the next step. signing_key must be an RSA private key,
* in must point to data to be digested and signed, and
* inlen must be the size of the data in bytes.
*/
ctx = EVP_PKEY_CTX_new(signing_key, NULL /* no engine */);
alg = EVP_SIGNATURE_fetch(NULL, "RSA-SHA256", NULL);
if (ctx == NULL || alg == NULL)
/* Error occurred */
if (EVP_PKEY_sign_message_init(ctx, alg, NULL) <= 0)
/* Error */
while (inlen > 0) {
if (EVP_PKEY_sign_message_update(ctx, in, inlen)) <= 0)
/* Error */
if (inlen > 256) {
inlen -= 256;
in += 256;
} else {
inlen = 0;
}
}
/* Determine sig buffer length */
if (EVP_PKEY_sign_message_final(ctx, NULL, &siglen) <= 0)
/* Error */
sig = OPENSSL_malloc(siglen);
if (sig == NULL)
/* malloc failure */
if (EVP_PKEY_sign_message_final(ctx, sig, &siglen) <= 0)
/* Error */
/* Signature is siglen bytes written to buffer sig */
SEE ALSO
EVP_PKEY_CTX_new(3), EVP_PKEY_CTX_ctrl(3), EVP_PKEY_encrypt(3),
EVP_PKEY_decrypt(3), EVP_PKEY_verify(3), EVP_PKEY_verify_recover(3),
EVP_PKEY_derive(3)
HISTORY
The EVP_PKEY_sign(3) functions were added in
OpenSSL 1.0.0.
The EVP_PKEY_sign_init_ex() function was added in OpenSSL 3.0.
The EVP_PKEY_sign_init_ex2(), EVP_PKEY_sign_message_init(),
EVP_PKEY_sign_message_update() and EVP_PKEY_sign_message_final()
functions where added in OpenSSL 3.4.
COPYRIGHT
Copyright 2006-2024 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
<https://www.openssl.org/source/license.html>.
3.4.0 2024-10-29 EVP_PKEY_SIGN(3ossl)
openssl 3.4.0 - Generated Thu Nov 7 12:12:36 CST 2024