oracular (3) EVP_DigestSignFinal.3ssl.gz

Provided by: libssl-doc_3.3.1-2ubuntu2.1_all bug

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 *sig,
                           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() is similar to a single call to EVP_DigestSignUpdate() and EVP_DigestSignFinal().  Unless
       sig is NULL, EVP_DigestSign() signs the data tbs of length tbslen bytes and places the signature in a
       buffer sig of size siglen.  If sig is NULL, the maximum necessary size of the signature buffer is written
       to the siglen parameter.


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.  Applications may disable this behavior by setting the EVP_MD_CTX_FLAG_FINALISE context
       flag via EVP_MD_CTX_set_flags(3).

       Note that not all providers support continuation, in case the selected provider does not allow to
       duplicate contexts EVP_DigestSignFinal() will finalize the digest context and attempting to process
       additional data via EVP_DigestSignUpdate() will result in an error.

       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.

       EVP_DigestSign() can not be called again, once a signature is generated (by passing sig as non NULL),
       unless the EVP_MD_CTX is reinitialised by calling EVP_DigestSignInit_ex().

       Ignoring failure returns of EVP_DigestSignInit() and EVP_DigestSignInit_ex() functions can lead to
       subsequent undefined behavior when calling EVP_DigestSignUpdate(), EVP_DigestSignFinal(), or
       EVP_DigestSign().

       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 2006-2024 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>.