- NAME
- SYNOPSIS
- DESCRIPTION
- NOTES
- RETURN VALUES
- EXAMPLE
- SEE ALSO
- HISTORY

# 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, EVP_PKEY_encrypt, EVP_PKEY_decrypt, EVP_PKEY_verify, EVP_PKEY_verify_recover, EVP_PKEY_derive

# HISTORY

These functions were first added to OpenSSL 1.0.0.