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

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

       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>

        EVP_PKEY_CTX *ctx;
        unsigned char *md, *sig;
        size_t mdlen, siglen;
        EVP_PKEY *signing_key;
        /* NB: assumes signing_key, md and mdlen are already set up
         * and that signing_key is an RSA private key
         */
        ctx = EVP_PKEY_CTX_new(signing_key);
        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_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.