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

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 oper-
       ations can be performed to set any appropriate parameters for the oper-
       ation (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 indi-
       cates 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>

        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                            2019-09-10                  EVP_PKEY_sign(3)
See also EVP_PKEY_sign_init(3)