| 1 | =pod
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| 2 |
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| 3 | =head1 NAME
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| 4 |
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| 5 | EVP_VerifyInit_ex,
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| 6 | EVP_VerifyInit, EVP_VerifyUpdate, EVP_VerifyFinal
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| 7 | - EVP signature verification functions
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| 8 |
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| 9 | =head1 SYNOPSIS
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| 10 |
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| 11 | #include <openssl/evp.h>
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| 12 |
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| 13 | int EVP_VerifyInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
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| 14 | int EVP_VerifyUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt);
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| 15 | int EVP_VerifyFinal(EVP_MD_CTX *ctx, unsigned char *sigbuf, unsigned int siglen,
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| 16 | EVP_PKEY *pkey);
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| 17 |
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| 18 | int EVP_VerifyInit(EVP_MD_CTX *ctx, const EVP_MD *type);
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| 19 |
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| 20 | =head1 DESCRIPTION
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| 21 |
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| 22 | The EVP signature verification routines are a high-level interface to digital
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| 23 | signatures.
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| 24 |
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| 25 | EVP_VerifyInit_ex() sets up verification context B<ctx> to use digest
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| 26 | B<type> from ENGINE B<impl>. B<ctx> must be created by calling
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| 27 | EVP_MD_CTX_new() before calling this function.
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| 28 |
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| 29 | EVP_VerifyUpdate() hashes B<cnt> bytes of data at B<d> into the
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| 30 | verification context B<ctx>. This function can be called several times on the
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| 31 | same B<ctx> to include additional data.
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| 32 |
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| 33 | EVP_VerifyFinal() verifies the data in B<ctx> using the public key B<pkey>
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| 34 | and against the B<siglen> bytes at B<sigbuf>.
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| 35 |
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| 36 | EVP_VerifyInit() initializes verification context B<ctx> to use the default
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| 37 | implementation of digest B<type>.
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| 38 |
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| 39 | =head1 RETURN VALUES
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| 40 |
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| 41 | EVP_VerifyInit_ex() and EVP_VerifyUpdate() return 1 for success and 0 for
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| 42 | failure.
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| 43 |
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| 44 | EVP_VerifyFinal() returns 1 for a correct signature, 0 for failure and -1 if some
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| 45 | other error occurred.
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| 46 |
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| 47 | The error codes can be obtained by L<ERR_get_error(3)>.
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| 48 |
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| 49 | =head1 NOTES
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| 50 |
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| 51 | The B<EVP> interface to digital signatures should almost always be used in
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| 52 | preference to the low-level interfaces. This is because the code then becomes
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| 53 | transparent to the algorithm used and much more flexible.
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| 54 |
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| 55 | The call to EVP_VerifyFinal() internally finalizes a copy of the digest context.
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| 56 | This means that calls to EVP_VerifyUpdate() and EVP_VerifyFinal() can be called
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| 57 | later to digest and verify additional data.
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| 58 |
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| 59 | Since only a copy of the digest context is ever finalized the context must
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| 60 | be cleaned up after use by calling EVP_MD_CTX_free() or a memory leak
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| 61 | will occur.
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| 62 |
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| 63 | =head1 BUGS
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| 64 |
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| 65 | Older versions of this documentation wrongly stated that calls to
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| 66 | EVP_VerifyUpdate() could not be made after calling EVP_VerifyFinal().
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| 67 |
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| 68 | Since the public key is passed in the call to EVP_SignFinal() any error
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| 69 | relating to the private key (for example an unsuitable key and digest
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| 70 | combination) will not be indicated until after potentially large amounts of
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| 71 | data have been passed through EVP_SignUpdate().
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| 72 |
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| 73 | It is not possible to change the signing parameters using these function.
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| 74 |
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| 75 | The previous two bugs are fixed in the newer EVP_DigestVerify*() function.
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| 76 |
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| 77 | =head1 SEE ALSO
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| 78 |
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| 79 | L<evp(7)>,
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| 80 | L<EVP_SignInit(3)>,
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| 81 | L<EVP_DigestInit(3)>,
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| 82 | L<evp(7)>, L<HMAC(3)>, L<MD2(3)>,
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| 83 | L<MD5(3)>, L<MDC2(3)>, L<RIPEMD160(3)>,
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| 84 | L<SHA1(3)>, L<dgst(1)>
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| 85 |
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| 86 | =head1 COPYRIGHT
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| 87 |
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| 88 | Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved.
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| 89 |
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| 90 | Licensed under the OpenSSL license (the "License"). You may not use
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| 91 | this file except in compliance with the License. You can obtain a copy
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| 92 | in the file LICENSE in the source distribution or at
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| 93 | L<https://www.openssl.org/source/license.html>.
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| 94 |
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| 95 | =cut
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