Cryptography and SSL/TLS Toolkit



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


 #include <openssl/evp.h>

 int EVP_PKEY_sign_init_ex(EVP_PKEY_CTX *ctx, EVP_SIGNATURE *signature);
 int EVP_PKEY_sign_init(EVP_PKEY_CTX *ctx);
 int EVP_PKEY_sign(EVP_PKEY_CTX *ctx,
                   unsigned char *sig, size_t *siglen,
                   const unsigned char *tbs, size_t tbslen);


The EVP_PKEY_sign_init_ex() function initializes a public key algorithm context for performing signing using the signature algorithm signature. The signature algorithm signature should be fetched using a call to EVP_SIGNATURE_fetch(3). The EVP_PKEY object associated with ctx must be compatible with that algorithm. signature may be NULL in which case the EVP_SIGNATURE algorithm is fetched implicitly based on the type of EVP_PKEY associated with ctx. See "Implicit fetch" in provider(7) for more information about implict fetches.

The EVP_PKEY_sign_init() function is the same as EVP_PKEY_sign_init_ex() except that the EVP_SIGNATURE algorithm is always implicitly fetched.

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.


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.


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.


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

 #include <openssl/evp.h>
 #include <openssl/rsa.h>

 /* 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 */


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)


EVP_PKEY_sign_init_ex() was added in OpenSSL 3.0. These functions were added in OpenSSL 1.0.0.

Copyright 2006-2016 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