Provided by: libssl-doc_3.4.1-1ubuntu3_all 
NAME
EVP_DigestVerifyInit_ex, EVP_DigestVerifyInit, EVP_DigestVerifyUpdate, EVP_DigestVerifyFinal,
EVP_DigestVerify - EVP signature verification functions
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 *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 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.
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_DigestVerifyFinal() will finalize the digest context and attempting to process
additional data via EVP_DigestVerifyUpdate() will result in an error.
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.
EVP_DigestVerify() can only be called once, and cannot be used again without reinitialising the
EVP_MD_CTX by calling EVP_DigestVerifyInit_ex().
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 2006-2024 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>.
3.4.1 2025-04-03 EVP_DIGESTVERIFYINIT(3SSL)