1EVP_DigestVerifyInit(3)             OpenSSL            EVP_DigestVerifyInit(3)
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NAME

6       EVP_DigestVerifyInit, EVP_DigestVerifyUpdate, EVP_DigestVerifyFinal -
7       EVP signature verification functions
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SYNOPSIS

10        #include <openssl/evp.h>
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12        int EVP_DigestVerifyInit(EVP_MD_CTX *ctx, EVP_PKEY_CTX **pctx,
13                               const EVP_MD *type, ENGINE *e, EVP_PKEY *pkey);
14        int EVP_DigestVerifyUpdate(EVP_MD_CTX *ctx, const void *d, size_t cnt);
15        int EVP_DigestVerifyFinal(EVP_MD_CTX *ctx, const unsigned char *sig, size_t siglen);
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DESCRIPTION

18       The EVP signature routines are a high level interface to digital
19       signatures.
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21       EVP_DigestVerifyInit() sets up verification context ctx to use digest
22       type from ENGINE impl and public key pkey. ctx must be initialized with
23       EVP_MD_CTX_init() before calling this function. If pctx is not NULL the
24       EVP_PKEY_CTX of the verification operation will be written to *pctx:
25       this can be used to set alternative verification options.
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27       EVP_DigestVerifyUpdate() hashes cnt bytes of data at d into the
28       verification context ctx. This function can be called several times on
29       the same ctx to include additional data. This function is currently
30       implemented using a macro.
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32       EVP_DigestVerifyFinal() verifies the data in ctx against the signature
33       in sig of length siglen.
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RETURN VALUES

36       EVP_DigestVerifyInit() and EVP_DigestVerifyUpdate() return 1 for
37       success and 0 or a negative value for failure. In particular a return
38       value of -2 indicates the operation is not supported by the public key
39       algorithm.
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41       EVP_DigestVerifyFinal() returns 1 for success; any other value
42       indicates failure.  A return value of zero indicates that the signature
43       did not verify successfully (that is, tbs did not match the original
44       data or the signature had an invalid form), while other values indicate
45       a more serious error (and sometimes also indicate an invalid signature
46       form).
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48       The error codes can be obtained from ERR_get_error(3).
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NOTES

51       The EVP interface to digital signatures should almost always be used in
52       preference to the low level interfaces. This is because the code then
53       becomes transparent to the algorithm used and much more flexible.
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55       In previous versions of OpenSSL there was a link between message digest
56       types and public key algorithms. This meant that "clone" digests such
57       as EVP_dss1() needed to be used to sign using SHA1 and DSA. This is no
58       longer necessary and the use of clone digest is now discouraged.
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60       For some key types and parameters the random number generator must be
61       seeded or the operation will fail.
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63       The call to EVP_DigestVerifyFinal() internally finalizes a copy of the
64       digest context. This means that EVP_VerifyUpdate() and
65       EVP_VerifyFinal() can be called later to digest and verify additional
66       data.
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68       Since only a copy of the digest context is ever finalized the context
69       must be cleaned up after use by calling EVP_MD_CTX_cleanup() or a
70       memory leak will occur.
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SEE ALSO

73       EVP_DigestSignInit(3), EVP_DigestInit(3), err(3), evp(3), hmac(3),
74       md2(3), md5(3), mdc2(3), ripemd(3), sha(3), dgst(1)
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HISTORY

77       EVP_DigestVerifyInit(), EVP_DigestVerifyUpdate() and
78       EVP_DigestVerifyFinal() were first added to OpenSSL 1.0.0.
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821.0.2o                            2019-09-10           EVP_DigestVerifyInit(3)