Updated: 2021/Apr/14


EVP_DigestSignInit(3)               OpenSSL              EVP_DigestSignInit(3)



NAME
       EVP_DigestSignInit, EVP_DigestSignUpdate, EVP_DigestSignFinal,
       EVP_DigestSign - EVP signing functions

LIBRARY
       libcrypto, -lcrypto

SYNOPSIS
        #include <openssl/evp.h>

        int EVP_DigestSignInit(EVP_MD_CTX *ctx, EVP_PKEY_CTX **pctx,
                               const EVP_MD *type, ENGINE *e, EVP_PKEY *pkey);
        int EVP_DigestSignUpdate(EVP_MD_CTX *ctx, const void *d, size_t cnt);
        int EVP_DigestSignFinal(EVP_MD_CTX *ctx, unsigned char *sig, size_t *siglen);

        int EVP_DigestSign(EVP_MD_CTX *ctx, unsigned char *sigret,
                           size_t *siglen, const unsigned char *tbs,
                           size_t tbslen);

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

       EVP_DigestSignInit() sets up signing context ctx to use digest type
       from ENGINE e and private key pkey. ctx must be created with
       EVP_MD_CTX_new() before calling this function. If pctx is not NULL, the
       EVP_PKEY_CTX of the signing operation will be written to *pctx: this
       can be used to set alternative signing options. Note that any existing
       value in *pctx is overwritten. The EVP_PKEY_CTX value returned must not
       be freed directly by the application if ctx is not assigned an
       EVP_PKEY_CTX value before being passed to EVP_DigestSignInit() (which
       means the EVP_PKEY_CTX is created inside EVP_DigestSignInit() and it
       will be freed automatically when the EVP_MD_CTX is freed).

       The digest type may be NULL if the signing algorithm supports it.

       No EVP_PKEY_CTX will be created by EVP_DigestSignInit() if the passed
       ctx has already been assigned one via EVP_MD_CTX_set_pkey_ctx(3). See
       also SM2(7).

       Only EVP_PKEY types that support signing can be used with these
       functions. This includes MAC algorithms where the MAC generation is
       considered as a form of "signing". Built-in EVP_PKEY types supported by
       these functions are CMAC, Poly1305, DSA, ECDSA, HMAC, RSA, SipHash,
       Ed25519 and Ed448.

       Not all digests can be used for all key types. The following
       combinations apply.

       DSA Supports SHA1, SHA224, SHA256, SHA384 and SHA512

       ECDSA
           Supports SHA1, SHA224, SHA256, SHA384, SHA512 and SM3

       RSA with no padding
           Supports no digests (the digest type must be NULL)

       RSA with X931 padding
           Supports SHA1, SHA256, SHA384 and SHA512

       All other RSA padding types
           Support SHA1, SHA224, SHA256, SHA384, SHA512, MD5, MD5_SHA1, MD2,
           MD4, MDC2, SHA3-224, SHA3-256, SHA3-384, SHA3-512

       Ed25519 and Ed448
           Support no digests (the digest type must be NULL)

       HMAC
           Supports any digest

       CMAC, Poly1305 and SipHash
           Will ignore any digest provided.

       If RSA-PSS is used and restrictions apply then the digest must match.

       EVP_DigestSignUpdate() 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. This function is currently implemented
       using a macro.

       EVP_DigestSignFinal() signs the data in ctx and places the signature in
       sig.  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.

       EVP_DigestSign() signs tbslen bytes of data at tbs and places the
       signature in sig and its length in siglen in a similar way to
       EVP_DigestSignFinal().

RETURN VALUES
       EVP_DigestSignInit(), EVP_DigestSignUpdate(), EVP_DigestSignFinal() and
       EVP_DigestSign() return 1 for success and 0 for failure.

       The error codes can be obtained from 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.

       EVP_DigestSign() is a one shot operation which signs a single block of
       data in one function. For algorithms that support streaming it is
       equivalent to calling EVP_DigestSignUpdate() and EVP_DigestSignFinal().
       For algorithms which do not support streaming (e.g. PureEdDSA) it is
       the only way to sign data.

       In previous versions of OpenSSL there was a link between message digest
       types and public key algorithms. This meant that "clone" digests such
       as EVP_dss1() needed to be used to sign using SHA1 and DSA. This is no
       longer necessary and the use of clone digest is now discouraged.

       For some key types and parameters 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_DigestSignFinal() internally finalizes a copy of the
       digest context. This means that calls to EVP_DigestSignUpdate() and
       EVP_DigestSignFinal() 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.

       The use of EVP_PKEY_size() with these functions is discouraged because
       some signature operations may have a signature length which depends on
       the parameters set. As a result EVP_PKEY_size() would have to return a
       value which indicates the maximum possible signature for any set of
       parameters.

SEE ALSO
       EVP_DigestVerifyInit(3), EVP_DigestInit(3), evp(7), HMAC(3), MD2(3),
       MD5(3), MDC2(3), RIPEMD160(3), SHA1(3), dgst(1), RAND(7)

HISTORY
       EVP_DigestSignInit(), EVP_DigestSignUpdate() and EVP_DigestSignFinal()
       were added in OpenSSL 1.0.0.

COPYRIGHT
       Copyright 2006-2020 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>.



1.1.1i                            2020-12-10             EVP_DigestSignInit(3)