openssl-prebuild/linux_amd64/ssl/share/man/man3/EVP_DigestVerifyInit.3
2020-03-02 16:50:34 +00:00

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.\" ========================================================================
.\"
.IX Title "EVP_DIGESTVERIFYINIT 3"
.TH EVP_DIGESTVERIFYINIT 3 "2020-03-02" "3.0.0-dev" "OpenSSL"
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.nh
.SH "NAME"
EVP_DigestVerifyInit_ex, EVP_DigestVerifyInit, EVP_DigestVerifyUpdate,
EVP_DigestVerifyFinal, EVP_DigestVerify \- EVP signature verification functions
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/evp.h>
\&
\& int EVP_DigestVerifyInit_ex(EVP_MD_CTX *ctx, EVP_PKEY_CTX **pctx,
\& const char *mdname, const char *props,
\& EVP_PKEY *pkey, EVP_SIGNATURE *signature);
\& 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);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The \s-1EVP\s0 signature routines are a high level interface to digital signatures.
Input data is digested first before the signature verification takes place.
.PP
\&\fIEVP_DigestVerifyInit_ex()\fR sets up verification context \fBctx\fR to use a digest
with the name \fBmdname\fR and public key \fBpkey\fR. The signature algorithm
\&\fBsignature\fR will be used for the actual signature verification which must be
compatible with the public key. 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 \fBprops\fR argument for the properties to
be used during the fetch.
.PP
The \fBsignature\fR parameter may be \s-1NULL\s0 in which case a suitable signature
algorithm implementation will be implicitly fetched based on the type of key in
use. See \fIprovider\fR\|(7) for further information about providers and fetching
algorithms.
.PP
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.
.PP
\&\fBctx\fR must be created with \fIEVP_MD_CTX_new()\fR before calling this function. If
\&\fBpctx\fR is not \s-1NULL\s0, the \s-1EVP_PKEY_CTX\s0 of the verification operation will be
written to \fB*pctx\fR: this can be used to set alternative verification options.
Note that any existing value in \fB*pctx\fR is overwritten. The \s-1EVP_PKEY_CTX\s0 value
returned must not be freed directly by the application if \fBctx\fR is not assigned
an \s-1EVP_PKEY_CTX\s0 value before being passed to \fIEVP_DigestVerifyInit_ex()\fR (which
means the \s-1EVP_PKEY_CTX\s0 is created inside \fIEVP_DigestVerifyInit_ex()\fR and it will
be freed automatically when the \s-1EVP_MD_CTX\s0 is freed).
.PP
No \fB\s-1EVP_PKEY_CTX\s0\fR will be created by \fIEVP_DigestSignInit_ex()\fR if the passed
\&\fBctx\fR has already been assigned one via \fIEVP_MD_CTX_set_pkey_ctx\fR\|(3). See also
\&\s-1\fISM2\s0\fR\|(7).
.PP
Not all digests can be used for all key types. The following combinations apply.
.IP "\s-1DSA\s0" 4
.IX Item "DSA"
Supports \s-1SHA1\s0, \s-1SHA224\s0, \s-1SHA256\s0, \s-1SHA384\s0 and \s-1SHA512\s0
.IP "\s-1ECDSA\s0" 4
.IX Item "ECDSA"
Supports \s-1SHA1\s0, \s-1SHA224\s0, \s-1SHA256\s0, \s-1SHA384\s0, \s-1SHA512\s0 and \s-1SM3\s0
.IP "\s-1RSA\s0 with no padding" 4
.IX Item "RSA with no padding"
Supports no digests (the digest \fBtype\fR must be \s-1NULL\s0)
.IP "\s-1RSA\s0 with X931 padding" 4
.IX Item "RSA with X931 padding"
Supports \s-1SHA1\s0, \s-1SHA256\s0, \s-1SHA384\s0 and \s-1SHA512\s0
.IP "All other \s-1RSA\s0 padding types" 4
.IX Item "All other RSA padding types"
Support \s-1SHA1\s0, \s-1SHA224\s0, \s-1SHA256\s0, \s-1SHA384\s0, \s-1SHA512\s0, \s-1MD5\s0, \s-1MD5_SHA1\s0, \s-1MD2\s0, \s-1MD4\s0, \s-1MDC2\s0,
\&\s-1SHA3\-224\s0, \s-1SHA3\-256\s0, \s-1SHA3\-384\s0, \s-1SHA3\-512\s0
.IP "Ed25519 and Ed448" 4
.IX Item "Ed25519 and Ed448"
Support no digests (the digest \fBtype\fR must be \s-1NULL\s0)
.IP "\s-1HMAC\s0" 4
.IX Item "HMAC"
Supports any digest
.IP "\s-1CMAC\s0, Poly1305 and SipHash" 4
.IX Item "CMAC, Poly1305 and SipHash"
Will ignore any digest provided.
.PP
If RSA-PSS is used and restrictions apply then the digest must match.
.PP
\&\fIEVP_DigestVerifyInit()\fR works in the same way as \fIEVP_DigestVerifyInit_ex()\fR except
that the \fBmdname\fR parameter will be inferred from the supplied digest \fBtype\fR,
and \fBprops\fR will be \s-1NULL\s0. Where supplied the \s-1ENGINE\s0 \fBe\fR will be used for the
signature verification and digest algorithm implementations. \fBe\fR may be \s-1NULL\s0.
.PP
\&\fIEVP_DigestVerifyUpdate()\fR hashes \fBcnt\fR bytes of data at \fBd\fR into the
verification context \fBctx\fR. This function can be called several times on the
same \fBctx\fR to include additional data.
.PP
\&\fIEVP_DigestVerifyFinal()\fR verifies the data in \fBctx\fR against the signature in
\&\fBsig\fR of length \fBsiglen\fR.
.PP
\&\fIEVP_DigestVerify()\fR verifies \fBtbslen\fR bytes at \fBtbs\fR against the signature
in \fBsig\fR of length \fBsiglen\fR.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fIEVP_DigestVerifyInit()\fR and \fIEVP_DigestVerifyUpdate()\fR return 1 for success and 0
for failure.
.PP
\&\fIEVP_DigestVerifyFinal()\fR and \fIEVP_DigestVerify()\fR return 1 for success; any other
value indicates failure. A return value of zero indicates that the signature
did not verify successfully (that is, \fBtbs\fR 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).
.PP
The error codes can be obtained from \fIERR_get_error\fR\|(3).
.SH "NOTES"
.IX Header "NOTES"
The \fB\s-1EVP\s0\fR 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.
.PP
\&\fIEVP_DigestVerify()\fR 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 \fIEVP_DigestVerifyUpdate()\fR and \fIEVP_DigestVerifyFinal()\fR. For
algorithms which do not support streaming (e.g. PureEdDSA) it is the only way
to verify data.
.PP
In previous versions of OpenSSL there was a link between message digest types
and public key algorithms. This meant that \*(L"clone\*(R" digests such as \fIEVP_dss1()\fR
needed to be used to sign using \s-1SHA1\s0 and \s-1DSA\s0. This is no longer necessary and
the use of clone digest is now discouraged.
.PP
For some key types and parameters the random number generator must be seeded.
If the automatic seeding or reseeding of the OpenSSL \s-1CSPRNG\s0 fails due to
external circumstances (see \s-1\fIRAND\s0\fR\|(7)), the operation will fail.
.PP
The call to \fIEVP_DigestVerifyFinal()\fR internally finalizes a copy of the digest
context. This means that \fIEVP_VerifyUpdate()\fR and \fIEVP_VerifyFinal()\fR can
be called later to digest and verify additional data.
.PP
Since only a copy of the digest context is ever finalized, the context must
be cleaned up after use by calling \fIEVP_MD_CTX_free()\fR or a memory leak
will occur.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fIEVP_DigestSignInit\fR\|(3),
\&\fIEVP_DigestInit\fR\|(3),
\&\fIevp\fR\|(7), \s-1\fIHMAC\s0\fR\|(3), \s-1\fIMD2\s0\fR\|(3),
\&\s-1\fIMD5\s0\fR\|(3), \s-1\fIMDC2\s0\fR\|(3), \s-1\fIRIPEMD160\s0\fR\|(3),
\&\s-1\fISHA1\s0\fR\|(3), \fIopenssl\-dgst\fR\|(1),
\&\s-1\fIRAND\s0\fR\|(7)
.SH "HISTORY"
.IX Header "HISTORY"
\&\fIEVP_DigestVerifyInit()\fR, \fIEVP_DigestVerifyUpdate()\fR and \fIEVP_DigestVerifyFinal()\fR
were added in OpenSSL 1.0.0.
.PP
\&\fIEVP_DigestVerifyInit_ex()\fR was added in OpenSSL 3.0.
.PP
\&\fIEVP_DigestVerifyUpdate()\fR was converted from a macro to a function in OpenSSL
3.0.
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2006\-2018 The OpenSSL Project Authors. All Rights Reserved.
.PP
Licensed under the Apache License 2.0 (the \*(L"License\*(R"). You may not use
this file except in compliance with the License. You can obtain a copy
in the file \s-1LICENSE\s0 in the source distribution or at
<https://www.openssl.org/source/license.html>.