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EVP_SIGNINIT(3)                     OpenSSL                    EVP_SIGNINIT(3)
NAME
       EVP_SignInit, EVP_SignInit_ex, EVP_SignUpdate, 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(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() signs the data in ctx using the private key pkey and
       places the signature in sig. sig must be at least "EVP_PKEY_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_size(pkey)"
       bytes will be written.
       EVP_SignInit() initializes a signing context ctx to use the default
       implementation of digest type.
RETURN VALUES
       EVP_SignInit_ex(), EVP_SignUpdate() 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_size(3), EVP_PKEY_bits(3), EVP_PKEY_security_bits(3),
       EVP_VerifyInit(3), EVP_DigestInit(3), evp(7), HMAC(3), MD2(3), MD5(3),
       MDC2(3), RIPEMD160(3), SHA1(3), dgst(1)
COPYRIGHT
       Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved.
       Licensed under the OpenSSL license (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>;.
1.1.1k                            2021-03-25                   EVP_SIGNINIT(3)