Updated: 2022/Sep/29

Please read Privacy Policy. It's for your privacy.

EVP_PKEY_sign(3)                    OpenSSL                   EVP_PKEY_sign(3)



NAME
       EVP_PKEY_sign_init, EVP_PKEY_sign_init_ex, EVP_PKEY_sign - sign using a
       public key algorithm

LIBRARY
       libcrypto, -lcrypto

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(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.

       The EVP_PKEY_sign() function performs a public key signing operation
       using ctx. The data to be signed is specified using the tbs and tbslen
       parameters. 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,
       if the call is successful the signature is written to sig and the
       amount of data written to siglen.

NOTES
       EVP_PKEY_sign() does not hash the data to be signed, and therefore is
       normally used to sign digests. For signing arbitrary messages, see the
       EVP_DigestSignInit(3) and EVP_SignInit(3) signing interfaces instead.

       After the call to EVP_PKEY_sign_init() algorithm specific control
       operations can be performed to set any appropriate parameters for the
       operation (see EVP_PKEY_CTX_ctrl(3)).

       The function EVP_PKEY_sign() can be called more than once on the same
       context if several operations are performed using the same parameters.

RETURN VALUES
       EVP_PKEY_sign_init() and EVP_PKEY_sign() return 1 for success and 0 or
       a negative value for failure. In particular a return value of -2
       indicates the operation is not supported by the public key algorithm.

EXAMPLES
       Sign data using RSA with PKCS#1 padding and SHA256 digest:

        #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)
            /* 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)
            /* malloc failure */

        if (EVP_PKEY_sign(ctx, sig, &siglen, md, mdlen) <= 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_init() and EVP_PKEY_sign() functions were added in
       OpenSSL 1.0.0.

       The EVP_PKEY_sign_init_ex() function was added in OpenSSL 3.0.

COPYRIGHT
       Copyright 2006-2021 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>.



3.0.12                            2023-05-07                  EVP_PKEY_sign(3)