115 lines
4.6 KiB
Plaintext
115 lines
4.6 KiB
Plaintext
=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_DigestSignInit() if the passed B<ctx>
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has already been assigned one via L<EVP_MD_CTX_set_pkey_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 2006-2020 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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