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| 1 | =pod | ||
| 2 | |||
| 3 | =head1 NAME | ||
| 4 | |||
| 5 | EVP_DigestVerifyInit, EVP_DigestVerifyUpdate, EVP_DigestVerifyFinal - EVP signature verification functions | ||
| 6 | |||
| 7 | =head1 SYNOPSIS | ||
| 8 | |||
| 9 | #include <openssl/evp.h> | ||
| 10 | |||
| 11 | int EVP_DigestVerifyInit(EVP_MD_CTX *ctx, EVP_PKEY_CTX **pctx, | ||
| 12 | const EVP_MD *type, ENGINE *e, EVP_PKEY *pkey); | ||
| 13 | int EVP_DigestVerifyUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt); | ||
| 14 | int EVP_DigestVerifyFinal(EVP_MD_CTX *ctx, unsigned char *sig, size_t siglen); | ||
| 15 | |||
| 16 | =head1 DESCRIPTION | ||
| 17 | |||
| 18 | The EVP signature routines are a high level interface to digital signatures. | ||
| 19 | |||
| 20 | EVP_DigestVerifyInit() sets up verification context B<ctx> to use digest | ||
| 21 | B<type> from ENGINE B<impl> and public key B<pkey>. B<ctx> must be initialized | ||
| 22 | with EVP_MD_CTX_init() before calling this function. If B<pctx> is not NULL the | ||
| 23 | EVP_PKEY_CTX of the verification operation will be written to B<*pctx>: this | ||
| 24 | can be used to set alternative verification options. | ||
| 25 | |||
| 26 | EVP_DigestVerifyUpdate() hashes B<cnt> bytes of data at B<d> into the | ||
| 27 | verification context B<ctx>. This function can be called several times on the | ||
| 28 | same B<ctx> to include additional data. This function is currently implemented | ||
| 29 | using a macro. | ||
| 30 | |||
| 31 | EVP_DigestVerifyFinal() verifies the data in B<ctx> against the signature in | ||
| 32 | B<sig> of length B<siglen>. | ||
| 33 | |||
| 34 | =head1 RETURN VALUES | ||
| 35 | |||
| 36 | EVP_DigestVerifyInit() and EVP_DigestVerifyUpdate() return 1 for success and 0 | ||
| 37 | or a negative value for failure. In particular a return value of -2 indicates | ||
| 38 | the operation is not supported by the public key algorithm. | ||
| 39 | |||
| 40 | Unlike other functions the return value 0 from EVP_DigestVerifyFinal() only | ||
| 41 | indicates that the signature did not not verify successfully (that is tbs did | ||
| 42 | not match the original data or the signature was of invalid form) it is not an | ||
| 43 | indication of a more serious error. | ||
| 44 | |||
| 45 | The error codes can be obtained from L<ERR_get_error(3)|ERR_get_error(3)>. | ||
| 46 | |||
| 47 | =head1 NOTES | ||
| 48 | |||
| 49 | The B<EVP> interface to digital signatures should almost always be used in | ||
| 50 | preference to the low level interfaces. This is because the code then becomes | ||
| 51 | transparent to the algorithm used and much more flexible. | ||
| 52 | |||
| 53 | In previous versions of OpenSSL there was a link between message digest types | ||
| 54 | and public key algorithms. This meant that "clone" digests such as EVP_dss1() | ||
| 55 | needed to be used to sign using SHA1 and DSA. This is no longer necessary and | ||
| 56 | the use of clone digest is now discouraged. | ||
| 57 | |||
| 58 | For some key types and parameters the random number generator must be seeded | ||
| 59 | or the operation will fail. | ||
| 60 | |||
| 61 | The call to EVP_DigestVerifyFinal() internally finalizes a copy of the digest | ||
| 62 | context. This means that calls to EVP_VerifyUpdate() and EVP_VerifyFinal() can | ||
| 63 | be called later to digest and verify additional data. | ||
| 64 | |||
| 65 | Since only a copy of the digest context is ever finalized the context must | ||
| 66 | be cleaned up after use by calling EVP_MD_CTX_cleanup() or a memory leak | ||
| 67 | will occur. | ||
| 68 | |||
| 69 | =head1 SEE ALSO | ||
| 70 | |||
| 71 | L<EVP_DigestSignInit(3)|EVP_DigestSignInit(3)>, | ||
| 72 | L<EVP_DigestInit(3)|EVP_DigestInit(3)>, L<err(3)|err(3)>, | ||
| 73 | L<evp(3)|evp(3)>, L<hmac(3)|hmac(3)>, L<md2(3)|md2(3)>, | ||
| 74 | L<md5(3)|md5(3)>, L<mdc2(3)|mdc2(3)>, L<ripemd(3)|ripemd(3)>, | ||
| 75 | L<sha(3)|sha(3)>, L<dgst(1)|dgst(1)> | ||
| 76 | |||
| 77 | =head1 HISTORY | ||
| 78 | |||
| 79 | EVP_DigestVerifyInit(), EVP_DigestVerifyUpdate() and EVP_DigestVerifyFinal() | ||
| 80 | were first added to OpenSSL 1.0.0. | ||
| 81 | |||
| 82 | =cut | ||
