1=pod 2 3=head1 NAME 4 5EVP_DigestSignInit_ex, EVP_DigestSignInit, EVP_DigestSignUpdate, 6EVP_DigestSignFinal, EVP_DigestSign - EVP signing functions 7 8=head1 SYNOPSIS 9 10 #include <openssl/evp.h> 11 12 int EVP_DigestSignInit_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_DigestSignInit(EVP_MD_CTX *ctx, EVP_PKEY_CTX **pctx, 17 const EVP_MD *type, ENGINE *e, EVP_PKEY *pkey); 18 int EVP_DigestSignUpdate(EVP_MD_CTX *ctx, const void *d, size_t cnt); 19 int EVP_DigestSignFinal(EVP_MD_CTX *ctx, unsigned char *sig, size_t *siglen); 20 21 int EVP_DigestSign(EVP_MD_CTX *ctx, unsigned char *sig, 22 size_t *siglen, const unsigned char *tbs, 23 size_t tbslen); 24 25=head1 DESCRIPTION 26 27The EVP signature routines are a high-level interface to digital signatures. 28Input data is digested first before the signing takes place. 29 30EVP_DigestSignInit_ex() sets up signing context I<ctx> to use a digest 31with the name I<mdname> and private key I<pkey>. The name of the digest to be 32used is passed to the provider of the signature algorithm in use. How that 33provider interprets the digest name is provider specific. The provider may 34implement that digest directly itself or it may (optionally) choose to fetch it 35(which could result in a digest from a different provider being selected). If the 36provider supports fetching the digest then it may use the I<props> argument for 37the properties to be used during the fetch. Finally, the passed parameters 38I<params>, if not NULL, are set on the context before returning. 39 40The I<pkey> algorithm is used to fetch a B<EVP_SIGNATURE> method implicitly, to 41be used for the actual signing. See L<provider(7)/Implicit fetch> for 42more information about implicit fetches. 43 44The OpenSSL default and legacy providers support fetching digests and can fetch 45those digests from any available provider. The OpenSSL FIPS provider also 46supports fetching digests but will only fetch digests that are themselves 47implemented inside the FIPS provider. 48 49I<ctx> must be created with EVP_MD_CTX_new() before calling this function. If 50I<pctx> is not NULL, the EVP_PKEY_CTX of the signing operation will be written 51to I<*pctx>: this can be used to set alternative signing options. Note that any 52existing value in I<*pctx> is overwritten. The EVP_PKEY_CTX value returned must 53not be freed directly by the application if I<ctx> is not assigned an 54EVP_PKEY_CTX value before being passed to EVP_DigestSignInit_ex() 55(which means the EVP_PKEY_CTX is created inside EVP_DigestSignInit_ex() 56and it will be freed automatically when the EVP_MD_CTX is freed). If the 57EVP_PKEY_CTX to be used is created by EVP_DigestSignInit_ex then it 58will use the B<OSSL_LIB_CTX> specified in I<libctx> and the property query string 59specified in I<props>. 60 61The digest I<mdname> may be NULL if the signing algorithm supports it. The 62I<props> argument can always be NULL. 63 64No B<EVP_PKEY_CTX> will be created by EVP_DigestSignInit_ex() if the 65passed I<ctx> has already been assigned one via L<EVP_MD_CTX_set_pkey_ctx(3)>. 66See also L<SM2(7)>. 67 68Only EVP_PKEY types that support signing can be used with these functions. This 69includes MAC algorithms where the MAC generation is considered as a form of 70"signing". Built-in EVP_PKEY types supported by these functions are CMAC, 71Poly1305, DSA, ECDSA, HMAC, RSA, SipHash, Ed25519 and Ed448. 72 73Not all digests can be used for all key types. The following combinations apply. 74 75=over 4 76 77=item DSA 78 79Supports SHA1, SHA224, SHA256, SHA384 and SHA512 80 81=item ECDSA 82 83Supports SHA1, SHA224, SHA256, SHA384, SHA512 and SM3 84 85=item RSA with no padding 86 87Supports no digests (the digest I<type> must be NULL) 88 89=item RSA with X931 padding 90 91Supports SHA1, SHA256, SHA384 and SHA512 92 93=item All other RSA padding types 94 95Support SHA1, SHA224, SHA256, SHA384, SHA512, MD5, MD5_SHA1, MD2, MD4, MDC2, 96SHA3-224, SHA3-256, SHA3-384, SHA3-512 97 98=item Ed25519 and Ed448 99 100Support no digests (the digest I<type> must be NULL) 101 102=item HMAC 103 104Supports any digest 105 106=item CMAC, Poly1305 and SipHash 107 108Will ignore any digest provided. 109 110=back 111 112If RSA-PSS is used and restrictions apply then the digest must match. 113 114EVP_DigestSignInit() works in the same way as EVP_DigestSignInit_ex() 115except that the I<mdname> parameter will be inferred from the supplied 116digest I<type>, and I<props> will be NULL. Where supplied the ENGINE I<e> will 117be used for the signing and digest algorithm implementations. I<e> may be NULL. 118 119EVP_DigestSignUpdate() hashes I<cnt> bytes of data at I<d> into the 120signature context I<ctx>. This function can be called several times on the 121same I<ctx> to include additional data. I<ctx> B<MUST NOT> be NULL. 122 123Unless I<sig> is NULL EVP_DigestSignFinal() signs the data in I<ctx> 124and places the signature in I<sig>. 125Otherwise the maximum necessary size of the output buffer is written to 126the I<siglen> parameter. If I<sig> is not NULL then before the call the 127I<siglen> parameter should contain the length of the I<sig> buffer. If the 128call is successful the signature is written to I<sig> and the amount of data 129written to I<siglen>. 130 131EVP_DigestSign() is similar to a single call to EVP_DigestSignUpdate() and 132EVP_DigestSignFinal(). 133Unless I<sig> is NULL, EVP_DigestSign() signs the data I<tbs> of length I<tbslen> 134bytes and places the signature in a buffer I<sig> of size I<siglen>. 135If I<sig> is NULL, the maximum necessary size of the signature buffer is written 136to the I<siglen> parameter. 137 138=head1 RETURN VALUES 139 140EVP_DigestSignInit(), EVP_DigestSignUpdate(), EVP_DigestSignFinal() and 141EVP_DigestSign() return 1 for success and 0 for failure. 142 143The error codes can be obtained from L<ERR_get_error(3)>. 144 145=head1 NOTES 146 147The B<EVP> interface to digital signatures should almost always be used in 148preference to the low-level interfaces. This is because the code then becomes 149transparent to the algorithm used and much more flexible. 150 151EVP_DigestSign() is a one shot operation which signs a single block of data 152in one function. For algorithms that support streaming it is equivalent to 153calling EVP_DigestSignUpdate() and EVP_DigestSignFinal(). For algorithms which 154do not support streaming (e.g. PureEdDSA) it is the only way to sign data. 155 156In previous versions of OpenSSL there was a link between message digest types 157and public key algorithms. This meant that "clone" digests such as EVP_dss1() 158needed to be used to sign using SHA1 and DSA. This is no longer necessary and 159the use of clone digest is now discouraged. 160 161For some key types and parameters the random number generator must be seeded. 162If the automatic seeding or reseeding of the OpenSSL CSPRNG fails due to 163external circumstances (see L<RAND(7)>), the operation will fail. 164 165The call to EVP_DigestSignFinal() internally finalizes a copy of the digest 166context. This means that calls to EVP_DigestSignUpdate() and 167EVP_DigestSignFinal() can be called later to digest and sign additional data. 168Applications may disable this behavior by setting the EVP_MD_CTX_FLAG_FINALISE 169context flag via L<EVP_MD_CTX_set_flags(3)>. 170 171Note that not all providers support continuation, in case the selected 172provider does not allow to duplicate contexts EVP_DigestSignFinal() will 173finalize the digest context and attempting to process additional data via 174EVP_DigestSignUpdate() will result in an error. 175 176EVP_DigestSignInit() and EVP_DigestSignInit_ex() functions can be called 177multiple times on a context and the parameters set by previous calls should be 178preserved if the I<pkey> parameter is NULL. The call then just resets the state 179of the I<ctx>. 180 181EVP_DigestSign() can not be called again, once a signature is generated (by 182passing I<sig> as non NULL), unless the B<EVP_MD_CTX> is reinitialised by 183calling EVP_DigestSignInit_ex(). 184 185Ignoring failure returns of EVP_DigestSignInit() and EVP_DigestSignInit_ex() 186functions can lead to subsequent undefined behavior when calling 187EVP_DigestSignUpdate(), EVP_DigestSignFinal(), or EVP_DigestSign(). 188 189The use of EVP_PKEY_get_size() with these functions is discouraged because some 190signature operations may have a signature length which depends on the 191parameters set. As a result EVP_PKEY_get_size() would have to return a value 192which indicates the maximum possible signature for any set of parameters. 193 194=head1 SEE ALSO 195 196L<EVP_DigestVerifyInit(3)>, 197L<EVP_DigestInit(3)>, 198L<evp(7)>, L<HMAC(3)>, L<MD2(3)>, 199L<MD5(3)>, L<MDC2(3)>, L<RIPEMD160(3)>, 200L<SHA1(3)>, L<openssl-dgst(1)>, 201L<RAND(7)> 202 203=head1 HISTORY 204 205EVP_DigestSignInit(), EVP_DigestSignUpdate() and EVP_DigestSignFinal() 206were added in OpenSSL 1.0.0. 207 208EVP_DigestSignInit_ex() was added in OpenSSL 3.0. 209 210EVP_DigestSignUpdate() was converted from a macro to a function in OpenSSL 3.0. 211 212=head1 COPYRIGHT 213 214Copyright 2006-2024 The OpenSSL Project Authors. All Rights Reserved. 215 216Licensed under the Apache License 2.0 (the "License"). You may not use 217this file except in compliance with the License. You can obtain a copy 218in the file LICENSE in the source distribution or at 219L<https://www.openssl.org/source/license.html>. 220 221=cut 222
