NAME

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

SYNOPSIS

        #include <openssl/evp.h>

        int EVP_DigestSignInit_ex(EVP_MD_CTX *ctx, EVP_PKEY_CTX **pctx,
                                  const char *mdname, OSSL_LIB_CTX *libctx,
                                  const char *props, EVP_PKEY *pkey,
                                  const OSSL_PARAM params[]);
        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.  Input data
       is digested first before the signing takes place.

       EVP_DigestSignInit_ex() sets up signing context ctx to use a digest with the name mdname
       and private key pkey. The name of the digest to be used is passed to the provider of the
       signature algorithm in use. How that provider interprets the digest name is provider
       specific. The provider may implement that digest directly itself or it may (optionally)
       choose to fetch it (which could result in a digest from a different provider being
       selected). If the provider supports fetching the digest then it may use the props argument
       for the properties to be used during the fetch. Finally, the passed parameters params, if
       not NULL, are set on the context before returning.

       The pkey algorithm is used to fetch a EVP_SIGNATURE method implicitly, to be used for the
       actual signing. See "Implicit fetch" in provider(7) for more information about implicit
       fetches.

       The OpenSSL default and legacy providers support fetching digests and can fetch those
       digests from any available provider. The OpenSSL FIPS provider also supports fetching
       digests but will only fetch digests that are themselves implemented inside the FIPS
       provider.

       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_ex() (which
       means the EVP_PKEY_CTX is created inside EVP_DigestSignInit_ex() and it will be freed
       automatically when the EVP_MD_CTX is freed). If the EVP_PKEY_CTX to be used is created by
       EVP_DigestSignInit_ex then it will use the OSSL_LIB_CTX specified in libctx and the
       property query string specified in props.

       The digest mdname may be NULL if the signing algorithm supports it. The props argument can
       always be NULL.

       No EVP_PKEY_CTX will be created by EVP_DigestSignInit_ex() 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_DigestSignInit() works in the same way as EVP_DigestSignInit_ex() except that the
       mdname parameter will be inferred from the supplied digest type, and props will be NULL.
       Where supplied the ENGINE e will be used for the signing and digest algorithm
       implementations. e may be NULL.

       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.

       Unless sig is NULL EVP_DigestSignFinal() signs the data in ctx and places the signature in
       sig.  Otherwise the maximum necessary 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(). In the event of a failure
       EVP_DigestSign() cannot be called again without reinitialising the EVP_MD_CTX. If sig is
       NULL before the call then siglen will be populated with the required size for the sig
       buffer. If sig is non-NULL before the call then siglen should contain the length of the
       sig buffer.

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.

       EVP_DigestSignInit() and EVP_DigestSignInit_ex() functions can be called multiple times on
       a context and the parameters set by previous calls should be preserved if the pkey
       parameter is NULL. The call then just resets the state of the ctx.

       The use of EVP_PKEY_get_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_get_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), openssl-dgst(1), RAND(7)

HISTORY

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

       EVP_DigestSignInit_ex() was added in OpenSSL 3.0.

       EVP_DigestSignUpdate() was converted from a macro to a function in OpenSSL 3.0.

COPYRIGHT

       Copyright 2006-2022 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>.