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EVP_DigestVerifyInit(3)             OpenSSL            EVP_DigestVerifyInit(3)



NAME
       EVP_DigestVerifyInit_ex, EVP_DigestVerifyInit, EVP_DigestVerifyUpdate,
       EVP_DigestVerifyFinal, EVP_DigestVerify - EVP signature verification
       functions

LIBRARY
       libcrypto, -lcrypto

SYNOPSIS
        #include <openssl/evp.h>

        int EVP_DigestVerifyInit_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_DigestVerifyInit(EVP_MD_CTX *ctx, EVP_PKEY_CTX **pctx,
                                 const EVP_MD *type, ENGINE *e, EVP_PKEY *pkey);
        int EVP_DigestVerifyUpdate(EVP_MD_CTX *ctx, const void *d, size_t cnt);
        int EVP_DigestVerifyFinal(EVP_MD_CTX *ctx, const unsigned char *sig,
                                  size_t siglen);
        int EVP_DigestVerify(EVP_MD_CTX *ctx, const 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 signature
       verification takes place.

       EVP_DigestVerifyInit_ex() sets up verification context ctx to use a
       digest with the name mdname and public 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 verification operation
       will be written to *pctx: this can be used to set alternative
       verification 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_DigestVerifyInit_ex() (which means the EVP_PKEY_CTX
       is created inside EVP_DigestVerifyInit_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_DigestVerifyInit_ex then it will use the
       OSSL_LIB_CTX specified in libctx and the property query string
       specified in props.

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

       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_DigestVerifyInit() works in the same way as
       EVP_DigestVerifyInit_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 signature verification and
       digest algorithm implementations. e may be NULL.

       EVP_DigestVerifyUpdate() hashes cnt bytes of data at d into the
       verification context ctx. This function can be called several times on
       the same ctx to include additional data.

       EVP_DigestVerifyFinal() verifies the data in ctx against the signature
       in sig of length siglen.

       EVP_DigestVerify() verifies tbslen bytes at tbs against the signature
       in sig of length siglen.

RETURN VALUES
       EVP_DigestVerifyInit() and EVP_DigestVerifyUpdate() return 1 for
       success and 0 for failure.

       EVP_DigestVerifyFinal() and EVP_DigestVerify() return 1 for success;
       any other value indicates failure.  A return value of zero indicates
       that the signature did not verify successfully (that is, tbs did not
       match the original data or the signature had an invalid form), while
       other values indicate a more serious error (and sometimes also indicate
       an invalid signature form).

       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_DigestVerify() is a one shot operation which verifies a single
       block of data in one function. For algorithms that support streaming it
       is equivalent to calling EVP_DigestVerifyUpdate() and
       EVP_DigestVerifyFinal(). For algorithms which do not support streaming
       (e.g. PureEdDSA) it is the only way to verify 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_DigestVerifyFinal() internally finalizes a copy of the
       digest context. This means that EVP_VerifyUpdate() and
       EVP_VerifyFinal() can be called later to digest and verify additional
       data.

       EVP_DigestVerifyInit() and EVP_DigestVerifyInit_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.

       Ignoring failure returns of EVP_DigestVerifyInit() and
       EVP_DigestVerifyInit_ex() functions can lead to subsequent undefined
       behavior when calling EVP_DigestVerifyUpdate(),
       EVP_DigestVerifyFinal(), or EVP_DigestVerify().

SEE ALSO
       EVP_DigestSignInit(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_DigestVerifyInit(), EVP_DigestVerifyUpdate() and
       EVP_DigestVerifyFinal() were added in OpenSSL 1.0.0.

       EVP_DigestVerifyInit_ex() was added in OpenSSL 3.0.

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

COPYRIGHT
       Copyright 2006-2023 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_DigestVerifyInit(3)