/usr/man/cat.3/EVP_PKEY_sign.3

EVP_PKEY_sign(3)             OpenSSL             EVP_PKEY_sign(3)

NAME

     EVP_PKEY_sign_init, EVP_PKEY_sign - sign using a public key
     algorithm

SYNOPSIS

      #include <openssl/evp.h>

      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);

DESCRIPTION

     The EVP_PKEY_sign_init() function initializes a public key
     algorithm context using key pkey for a signing operation.

     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.

EXAMPLE

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

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

1.0.2t               Last change: 2019-09-10                    1

EVP_PKEY_sign(3)             OpenSSL             EVP_PKEY_sign(3)

      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

     These functions were first added to OpenSSL 1.0.0.

1.0.2t               Last change: 2019-09-10                    2

See also EVP_PKEY_sign_init(3)