f987a4dd89
The manual pages require for some API functions that the 'random number
generator must be seeded' before calling the function. Initially, this
was meant literally, i.e. the OpenSSL CSPRNG had to be seeded manually
before calling these functions.
Since version 1.1.1, the CSPRNG is seeded automatically on first use,
so it's not the responsibility of the programmer anymore. Still, he
needs to be aware that the seeding might fail.
Reviewed-by: Paul Dale <paul.dale@oracle.com>
Reviewed-by: Tomas Mraz <tmraz@fedoraproject.org>
(Merged from https://github.com/openssl/openssl/pull/9257)
(cherry picked from commit 262c00882a)
114 lines
4.6 KiB
Text
114 lines
4.6 KiB
Text
=pod
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=head1 NAME
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EVP_DigestVerifyInit, EVP_DigestVerifyUpdate, EVP_DigestVerifyFinal,
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EVP_DigestVerify - EVP signature verification functions
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=head1 SYNOPSIS
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#include <openssl/evp.h>
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int EVP_DigestVerifyInit(EVP_MD_CTX *ctx, EVP_PKEY_CTX **pctx,
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const EVP_MD *type, ENGINE *e, EVP_PKEY *pkey);
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int EVP_DigestVerifyUpdate(EVP_MD_CTX *ctx, const void *d, size_t cnt);
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int EVP_DigestVerifyFinal(EVP_MD_CTX *ctx, const unsigned char *sig,
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size_t siglen);
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int EVP_DigestVerify(EVP_MD_CTX *ctx, const unsigned char *sigret,
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size_t siglen, const unsigned char *tbs, size_t tbslen);
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=head1 DESCRIPTION
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The EVP signature routines are a high level interface to digital signatures.
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EVP_DigestVerifyInit() sets up verification context B<ctx> to use digest
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B<type> from ENGINE B<e> and public key B<pkey>. B<ctx> must be created
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with EVP_MD_CTX_new() before calling this function. If B<pctx> is not NULL, the
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EVP_PKEY_CTX of the verification operation will be written to B<*pctx>: this
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can be used to set alternative verification options. Note that any existing
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value in B<*pctx> is overwritten. The EVP_PKEY_CTX value returned must not be freed
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directly by the application if B<ctx> is not assigned an EVP_PKEY_CTX value before
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being passed to EVP_DigestVerifyInit() (which means the EVP_PKEY_CTX is created
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inside EVP_DigestVerifyInit() and it will be freed automatically when the
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EVP_MD_CTX is freed).
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No B<EVP_PKEY_CTX> will be created by EVP_DigsetSignInit() if the passed B<ctx>
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has already been assigned one via L<EVP_MD_CTX_set_ctx(3)>. See also L<SM2(7)>.
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EVP_DigestVerifyUpdate() hashes B<cnt> bytes of data at B<d> into the
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verification context B<ctx>. This function can be called several times on the
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same B<ctx> to include additional data. This function is currently implemented
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using a macro.
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EVP_DigestVerifyFinal() verifies the data in B<ctx> against the signature in
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B<sig> of length B<siglen>.
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EVP_DigestVerify() verifies B<tbslen> bytes at B<tbs> against the signature
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in B<sig> of length B<siglen>.
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=head1 RETURN VALUES
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EVP_DigestVerifyInit() and EVP_DigestVerifyUpdate() return 1 for success and 0
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for failure.
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EVP_DigestVerifyFinal() and EVP_DigestVerify() return 1 for success; any other
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value indicates failure. A return value of zero indicates that the signature
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did not verify successfully (that is, B<tbs> did not match the original data or
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the signature had an invalid form), while other values indicate a more serious
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error (and sometimes also indicate an invalid signature form).
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The error codes can be obtained from L<ERR_get_error(3)>.
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=head1 NOTES
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The B<EVP> interface to digital signatures should almost always be used in
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preference to the low level interfaces. This is because the code then becomes
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transparent to the algorithm used and much more flexible.
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EVP_DigestVerify() is a one shot operation which verifies a single block of
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data in one function. For algorithms that support streaming it is equivalent
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to calling EVP_DigestVerifyUpdate() and EVP_DigestVerifyFinal(). For
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algorithms which do not support streaming (e.g. PureEdDSA) it is the only way
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to verify data.
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In previous versions of OpenSSL there was a link between message digest types
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and public key algorithms. This meant that "clone" digests such as EVP_dss1()
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needed to be used to sign using SHA1 and DSA. This is no longer necessary and
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the use of clone digest is now discouraged.
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For some key types and parameters the random number generator must be seeded.
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If the automatic seeding or reseeding of the OpenSSL CSPRNG fails due to
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external circumstances (see L<RAND(7)>), the operation will fail.
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The call to EVP_DigestVerifyFinal() internally finalizes a copy of the digest
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context. This means that EVP_VerifyUpdate() and EVP_VerifyFinal() can
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be called later to digest and verify additional data.
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Since only a copy of the digest context is ever finalized, the context must
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be cleaned up after use by calling EVP_MD_CTX_free() or a memory leak
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will occur.
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=head1 SEE ALSO
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L<EVP_DigestSignInit(3)>,
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L<EVP_DigestInit(3)>,
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L<evp(7)>, L<HMAC(3)>, L<MD2(3)>,
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L<MD5(3)>, L<MDC2(3)>, L<RIPEMD160(3)>,
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L<SHA1(3)>, L<dgst(1)>,
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L<RAND(7)>
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=head1 HISTORY
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EVP_DigestVerifyInit(), EVP_DigestVerifyUpdate() and EVP_DigestVerifyFinal()
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were added in OpenSSL 1.0.0.
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=head1 COPYRIGHT
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Copyright 2006-2019 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the OpenSSL license (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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