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EVP_SignInit(3)                     OpenSSL                    EVP_SignInit(3)



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

LIBRARY
       libcrypto, -lcrypto

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 some private key types 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.

       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_DigestSign*()
       functions.

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>.



3.0.12                            2023-05-07                   EVP_SignInit(3)