NAME

       EVP_SignInit, EVP_SignInit_ex, EVP_SignUpdate, EVP_SignFinal_ex, EVP_SignFinal - EVP
       signing functions

SYNOPSIS

        #include <openssl/evp.h>

        int EVP_SignInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
        int EVP_SignUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt);
        int EVP_SignFinal_ex(EVP_MD_CTX *ctx, unsigned char *md, unsigned int *s,
                             EVP_PKEY *pkey, OSSL_LIB_CTX *libctx, const char *propq);
        int EVP_SignFinal(EVP_MD_CTX *ctx, unsigned char *sig, unsigned int *s,
                          EVP_PKEY *pkey);

        void EVP_SignInit(EVP_MD_CTX *ctx, const EVP_MD *type);

DESCRIPTION

       The EVP signature routines are a high-level interface to digital signatures.

       EVP_SignInit_ex() sets up signing context ctx to use digest type from ENGINE impl. ctx
       must be created with EVP_MD_CTX_new() before calling this function.

       EVP_SignUpdate() hashes cnt bytes of data at d into the signature context ctx. This
       function can be called several times on the same ctx to include additional data.

       EVP_SignFinal_ex() signs the data in ctx using the private key pkey and places the
       signature in sig. The library context libctx and property query propq are used when
       creating a context to use with the key pkey. sig must be at least
       "EVP_PKEY_get_size(pkey)" bytes in size.  s is an OUT parameter, and not used as an IN
       parameter.  The number of bytes of data written (i.e. the length of the signature) will be
       written to the integer at s, at most "EVP_PKEY_get_size(pkey)" bytes will be written.

       EVP_SignFinal() is similar to EVP_SignFinal_ex() but uses default values of NULL for the
       library context libctx and the property query propq.

       EVP_SignInit() initializes a signing context ctx to use the default implementation of
       digest type.

RETURN VALUES

       EVP_SignInit_ex(), EVP_SignUpdate(), EVP_SignFinal_ex() and EVP_SignFinal() return 1 for
       success and 0 for failure.

       The error codes can be obtained by ERR_get_error(3).

NOTES

       The EVP interface to digital signatures should almost always be used in preference to the
       low-level interfaces. This is because the code then becomes transparent to the algorithm
       used and much more flexible.

       When signing with DSA private keys the random number generator must be seeded.  If the
       automatic seeding or reseeding of the OpenSSL CSPRNG fails due to external circumstances
       (see RAND(7)), the operation will fail.  This requirement does not hold for RSA
       signatures.

       The call to EVP_SignFinal() internally finalizes a copy of the digest context.  This means
       that calls to EVP_SignUpdate() and EVP_SignFinal() can be called later to digest and sign
       additional data.

       Since only a copy of the digest context is ever finalized the context must be cleaned up
       after use by calling EVP_MD_CTX_free() or a memory leak will occur.

BUGS

       Older versions of this documentation wrongly stated that calls to EVP_SignUpdate() could
       not be made after calling EVP_SignFinal().

       Since the private key is passed in the call to EVP_SignFinal() any error relating to the
       private key (for example an unsuitable key and digest combination) will not be indicated
       until after potentially large amounts of data have been passed through EVP_SignUpdate().

       It is not possible to change the signing parameters using these function.

       The previous two bugs are fixed in the newer EVP_SignDigest*() function.

SEE ALSO

       EVP_PKEY_get_size(3), EVP_PKEY_get_bits(3), EVP_PKEY_get_security_bits(3),
       EVP_VerifyInit(3), EVP_DigestInit(3), evp(7), HMAC(3), MD2(3), MD5(3), MDC2(3),
       RIPEMD160(3), SHA1(3), openssl-dgst(1)

HISTORY

       The function EVP_SignFinal_ex() was added in OpenSSL 3.0.

COPYRIGHT

       Copyright 2000-2021 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 <https://www.openssl.org/source/license.html>.