1=pod 2 3=head1 NAME 4 5EVP_DigestVerifyInit_ex, EVP_DigestVerifyInit, EVP_DigestVerifyUpdate, 6EVP_DigestVerifyFinal, EVP_DigestVerify - EVP signature verification functions 7 8=head1 SYNOPSIS 9 10 #include <openssl/evp.h> 11 12 int EVP_DigestVerifyInit_ex(EVP_MD_CTX *ctx, EVP_PKEY_CTX **pctx, 13 const char *mdname, OSSL_LIB_CTX *libctx, 14 const char *props, EVP_PKEY *pkey, 15 const OSSL_PARAM params[]); 16 int EVP_DigestVerifyInit(EVP_MD_CTX *ctx, EVP_PKEY_CTX **pctx, 17 const EVP_MD *type, ENGINE *e, EVP_PKEY *pkey); 18 int EVP_DigestVerifyUpdate(EVP_MD_CTX *ctx, const void *d, size_t cnt); 19 int EVP_DigestVerifyFinal(EVP_MD_CTX *ctx, const unsigned char *sig, 20 size_t siglen); 21 int EVP_DigestVerify(EVP_MD_CTX *ctx, const unsigned char *sigret, 22 size_t siglen, const unsigned char *tbs, size_t tbslen); 23 24=head1 DESCRIPTION 25 26The EVP signature routines are a high-level interface to digital signatures. 27Input data is digested first before the signature verification takes place. 28 29EVP_DigestVerifyInit_ex() sets up verification context B<ctx> to use a 30digest with the name B<mdname> and public key B<pkey>. The name of the digest to 31be used is passed to the provider of the signature algorithm in use. How that 32provider interprets the digest name is provider specific. The provider may 33implement that digest directly itself or it may (optionally) choose to fetch it 34(which could result in a digest from a different provider being selected). If 35the provider supports fetching the digest then it may use the B<props> argument 36for the properties to be used during the fetch. Finally, the passed parameters 37I<params>, if not NULL, are set on the context before returning. 38 39The I<pkey> algorithm is used to fetch a B<EVP_SIGNATURE> method implicitly, to 40be used for the actual signing. See L<provider(7)/Implicit fetch> for 41more information about implicit fetches. 42 43The OpenSSL default and legacy providers support fetching digests and can fetch 44those digests from any available provider. The OpenSSL FIPS provider also 45supports fetching digests but will only fetch digests that are themselves 46implemented inside the FIPS provider. 47 48B<ctx> must be created with EVP_MD_CTX_new() before calling this function. If 49B<pctx> is not NULL, the EVP_PKEY_CTX of the verification operation will be 50written to B<*pctx>: this can be used to set alternative verification options. 51Note that any existing value in B<*pctx> is overwritten. The EVP_PKEY_CTX value 52returned must not be freed directly by the application if B<ctx> is not assigned 53an EVP_PKEY_CTX value before being passed to EVP_DigestVerifyInit_ex() 54(which means the EVP_PKEY_CTX is created inside 55EVP_DigestVerifyInit_ex() and it will be freed automatically when the 56EVP_MD_CTX is freed). If the EVP_PKEY_CTX to be used is created by 57EVP_DigestVerifyInit_ex then it will use the B<OSSL_LIB_CTX> specified 58in I<libctx> and the property query string specified in I<props>. 59 60No B<EVP_PKEY_CTX> will be created by EVP_DigestVerifyInit_ex() if the 61passed B<ctx> has already been assigned one via L<EVP_MD_CTX_set_pkey_ctx(3)>. 62See also L<SM2(7)>. 63 64Not all digests can be used for all key types. The following combinations apply. 65 66=over 4 67 68=item DSA 69 70Supports SHA1, SHA224, SHA256, SHA384 and SHA512 71 72=item ECDSA 73 74Supports SHA1, SHA224, SHA256, SHA384, SHA512 and SM3 75 76=item RSA with no padding 77 78Supports no digests (the digest B<type> must be NULL) 79 80=item RSA with X931 padding 81 82Supports SHA1, SHA256, SHA384 and SHA512 83 84=item All other RSA padding types 85 86Support SHA1, SHA224, SHA256, SHA384, SHA512, MD5, MD5_SHA1, MD2, MD4, MDC2, 87SHA3-224, SHA3-256, SHA3-384, SHA3-512 88 89=item Ed25519 and Ed448 90 91Support no digests (the digest B<type> must be NULL) 92 93=item HMAC 94 95Supports any digest 96 97=item CMAC, Poly1305 and Siphash 98 99Will ignore any digest provided. 100 101=back 102 103If RSA-PSS is used and restrictions apply then the digest must match. 104 105EVP_DigestVerifyInit() works in the same way as 106EVP_DigestVerifyInit_ex() except that the B<mdname> parameter will be 107inferred from the supplied digest B<type>, and B<props> will be NULL. Where 108supplied the ENGINE B<e> will be used for the signature verification and digest 109algorithm implementations. B<e> may be NULL. 110 111EVP_DigestVerifyUpdate() hashes B<cnt> bytes of data at B<d> into the 112verification context B<ctx>. This function can be called several times on the 113same B<ctx> to include additional data. 114 115EVP_DigestVerifyFinal() verifies the data in B<ctx> against the signature in 116B<sig> of length B<siglen>. 117 118EVP_DigestVerify() verifies B<tbslen> bytes at B<tbs> against the signature 119in B<sig> of length B<siglen>. 120 121=head1 RETURN VALUES 122 123EVP_DigestVerifyInit() and EVP_DigestVerifyUpdate() return 1 for success and 0 124for failure. 125 126EVP_DigestVerifyFinal() and EVP_DigestVerify() return 1 for success; any other 127value indicates failure. A return value of zero indicates that the signature 128did not verify successfully (that is, B<tbs> did not match the original data or 129the signature had an invalid form), while other values indicate a more serious 130error (and sometimes also indicate an invalid signature form). 131 132The error codes can be obtained from L<ERR_get_error(3)>. 133 134=head1 NOTES 135 136The B<EVP> interface to digital signatures should almost always be used in 137preference to the low-level interfaces. This is because the code then becomes 138transparent to the algorithm used and much more flexible. 139 140EVP_DigestVerify() is a one shot operation which verifies a single block of 141data in one function. For algorithms that support streaming it is equivalent 142to calling EVP_DigestVerifyUpdate() and EVP_DigestVerifyFinal(). For 143algorithms which do not support streaming (e.g. PureEdDSA) it is the only way 144to verify data. 145 146In previous versions of OpenSSL there was a link between message digest types 147and public key algorithms. This meant that "clone" digests such as EVP_dss1() 148needed to be used to sign using SHA1 and DSA. This is no longer necessary and 149the use of clone digest is now discouraged. 150 151For some key types and parameters the random number generator must be seeded. 152If the automatic seeding or reseeding of the OpenSSL CSPRNG fails due to 153external circumstances (see L<RAND(7)>), the operation will fail. 154 155The call to EVP_DigestVerifyFinal() internally finalizes a copy of the digest 156context. This means that EVP_VerifyUpdate() and EVP_VerifyFinal() can 157be called later to digest and verify additional data. 158 159EVP_DigestVerifyInit() and EVP_DigestVerifyInit_ex() functions can be called 160multiple times on a context and the parameters set by previous calls should be 161preserved if the I<pkey> parameter is NULL. The call then just resets the state 162of the I<ctx>. 163 164=head1 SEE ALSO 165 166L<EVP_DigestSignInit(3)>, 167L<EVP_DigestInit(3)>, 168L<evp(7)>, L<HMAC(3)>, L<MD2(3)>, 169L<MD5(3)>, L<MDC2(3)>, L<RIPEMD160(3)>, 170L<SHA1(3)>, L<openssl-dgst(1)>, 171L<RAND(7)> 172 173=head1 HISTORY 174 175EVP_DigestVerifyInit(), EVP_DigestVerifyUpdate() and EVP_DigestVerifyFinal() 176were added in OpenSSL 1.0.0. 177 178EVP_DigestVerifyInit_ex() was added in OpenSSL 3.0. 179 180EVP_DigestVerifyUpdate() was converted from a macro to a function in OpenSSL 1813.0. 182 183=head1 COPYRIGHT 184 185Copyright 2006-2022 The OpenSSL Project Authors. All Rights Reserved. 186 187Licensed under the Apache License 2.0 (the "License"). You may not use 188this file except in compliance with the License. You can obtain a copy 189in the file LICENSE in the source distribution or at 190L<https://www.openssl.org/source/license.html>. 191 192=cut 193