1=pod 2 3=head1 NAME 4 5EVP_PKEY_sign_init, EVP_PKEY_sign_init_ex, EVP_PKEY_sign_init_ex2, 6EVP_PKEY_sign, EVP_PKEY_sign_message_init, EVP_PKEY_sign_message_update, 7EVP_PKEY_sign_message_final - sign using a public key algorithm 8 9=head1 SYNOPSIS 10 11 #include <openssl/evp.h> 12 13 int EVP_PKEY_sign_init(EVP_PKEY_CTX *ctx); 14 int EVP_PKEY_sign_init_ex(EVP_PKEY_CTX *ctx, const OSSL_PARAM params[]); 15 int EVP_PKEY_sign_init_ex2(EVP_PKEY_CTX *ctx, EVP_SIGNATURE *algo, 16 const OSSL_PARAM params[]); 17 int EVP_PKEY_sign_message_init(EVP_PKEY_CTX *ctx, EVP_SIGNATURE *algo, 18 const OSSL_PARAM params[]); 19 int EVP_PKEY_sign_message_update(EVP_PKEY_CTX *ctx, 20 unsigned char *in, size_t inlen); 21 int EVP_PKEY_sign_message_final(EVP_PKEY_CTX *ctx, unsigned char *sig, 22 size_t *siglen, size_t sigsize); 23 int EVP_PKEY_sign(EVP_PKEY_CTX *ctx, 24 unsigned char *sig, size_t *siglen, 25 const unsigned char *tbs, size_t tbslen); 26 27=head1 DESCRIPTION 28 29EVP_PKEY_sign_init() initializes a public key algorithm context I<ctx> for 30signing using the algorithm given when the context was created 31using L<EVP_PKEY_CTX_new(3)> or variants thereof. The algorithm is used to 32fetch a B<EVP_SIGNATURE> method implicitly, see L<provider(7)/Implicit fetch> 33for more information about implicit fetches. 34 35EVP_PKEY_sign_init_ex() is the same as EVP_PKEY_sign_init() but additionally 36sets the passed parameters I<params> on the context before returning. 37 38EVP_PKEY_sign_init_ex2() initializes a public key algorithm context I<ctx> for 39signing a pre-computed message digest using the algorithm given by I<algo> and 40the key given through L<EVP_PKEY_CTX_new(3)> or L<EVP_PKEY_CTX_new_from_pkey(3)>. 41A context I<ctx> without a pre-loaded key cannot be used with this function. 42This function provides almost the same functionality as EVP_PKEY_sign_init_ex(), 43but is uniquely intended to be used with a pre-computed messsage digest, and 44allows pre-determining the exact conditions for that message digest, if a 45composite signature algorithm (such as RSA-SHA256) was fetched. 46Following a call to this function, setting parameters that modifies the digest 47implementation or padding is not normally supported. 48 49EVP_PKEY_sign_message_init() initializes a public key algorithm context I<ctx> 50for signing an unlimited size message using the algorithm given by I<algo> and 51the key given through L<EVP_PKEY_CTX_new(3)> or L<EVP_PKEY_CTX_new_from_pkey(3)>. 52Passing the message is supported both in a one-shot fashion using 53EVP_PKEY_sign(), and through the combination of EVP_PKEY_sign_message_update() 54and EVP_PKEY_sign_message_final(). 55This function enables using algorithms that can process input of arbitrary 56length, such as ED25519, RSA-SHA256 and similar. 57 58EVP_PKEY_sign_message_update() adds I<inlen> bytes from I<in> to the data to be 59processed for signature. The signature algorithm specification and 60implementation determine how the input bytes are processed and if there's a 61limit on the total size of the input. See L</NOTES> below for a deeper 62explanation. 63 64EVP_PKEY_sign_message_final() signs the processed data and places the data in 65I<sig>, and the number of signature bytes in I<*siglen>, if the number of 66bytes doesn't surpass the size given by I<sigsize>. 67I<sig> may be NULL, and in that case, only I<*siglen> is updated with the 68number of signature bytes. 69 70EVP_PKEY_sign() is a one-shot function that can be used with all the init 71functions above. 72When initialization was done with EVP_PKEY_sign_init(), EVP_PKEY_sign_init_ex() 73or EVP_PKEY_sign_init_ex2(), the data specified by I<tbs> and I<tbslen> is 74signed after appropriate padding. 75When initialization was done with EVP_PKEY_sign_message_init(), the data 76specified by I<tbs> and I<tbslen> is digested by the implied message digest 77algorithm, and the result is signed after appropriate padding. 78If I<sig> is NULL then the maximum size of the output buffer is written to the 79I<siglen> parameter. 80If I<sig> is not NULL, then before the call the I<siglen> parameter should 81contain the length of the I<sig> buffer, and if the call is successful the 82signature is written to I<sig> and the amount of data written to I<siglen>. 83 84=head1 NOTES 85 86=begin comment 87 88These notes are largely replicated in EVP_PKEY_verify.pod, please keep them 89in sync. 90 91=end comment 92 93=head2 General 94 95Some signature implementations only accumulate the input data and do no 96further processing before signing it (they expect the input to be a digest), 97while others compress the data, typically by internally producing a digest, 98and signing the result. 99Some of them support both modes of operation at the same time. 100The caller is expected to know how the chosen algorithm is supposed to behave 101and under what conditions. 102 103For example, an RSA implementation can be expected to only expect a message 104digest as input, while ED25519 can be expected to process the input with a hash, 105i.e. to produce the message digest internally, and while RSA-SHA256 can be 106expected to handle either mode of operation, depending on if the operation was 107initialized with EVP_PKEY_sign_init_ex2() or with EVP_PKEY_sign_message_init(). 108 109Similarly, an RSA implementation usually expects additional details to be set, 110like the message digest algorithm that the input is supposed to be digested 111with, as well as the padding mode (see L<EVP_PKEY_CTX_set_signature_md(3)> and 112L<EVP_PKEY_CTX_set_rsa_padding(3)> and similar others), while an RSA-SHA256 113implementation usually has these details pre-set and immutable. 114 115The functions described here can't be used to combine separate algorithms. In 116particular, neither L<EVP_PKEY_CTX_set_signature_md(3)> nor the B<OSSL_PARAM> 117parameter "digest" (B<OSSL_SIGNATURE_PARAM_DIGEST>) can be used to combine a 118signature algorithm with a hash algorithm to process the input. In other 119words, it's not possible to specify a I<ctx> pre-loaded with an RSA pkey, or 120an I<algo> that fetched C<RSA> and try to specify SHA256 separately to get the 121functionality of RSA-SHA256. If combining algorithms in that manner is 122desired, please use L<EVP_DigestSignInit(3)> and associated functions. 123 124=head2 Performing multiple signatures 125 126When initialized using EVP_PKEY_sign_init_ex() or EVP_PKEY_sign_init_ex2(), 127EVP_PKEY_sign() can be called more than once on the same context to have 128several one-shot operations performed using the same parameters. 129 130When initialized using EVP_PKEY_sign_message_init(), it's not possible to 131call EVP_PKEY_sign() multiple times. 132 133=head1 RETURN VALUES 134 135All functions return 1 for success and 0 or a negative value for failure. 136 137In particular, EVP_PKEY_sign_init() and its other variants may return -2 to 138indicate that the operation is not supported by the public key algorithm. 139 140=head1 EXAMPLES 141 142=begin comment 143 144These examples are largely replicated in EVP_PKEY_verify.pod, please keep them 145in sync. 146 147=end comment 148 149=head2 RSA with PKCS#1 padding for SHA256 150 151Sign data using RSA with PKCS#1 padding and a SHA256 digest as input: 152 153 #include <openssl/evp.h> 154 #include <openssl/rsa.h> 155 156 EVP_PKEY_CTX *ctx; 157 /* md is a SHA-256 digest in this example. */ 158 unsigned char *md, *sig; 159 size_t mdlen = 32, siglen; 160 EVP_PKEY *signing_key; 161 162 /* 163 * NB: assumes signing_key and md are set up before the next 164 * step. signing_key must be an RSA private key and md must 165 * point to the SHA-256 digest to be signed. 166 */ 167 ctx = EVP_PKEY_CTX_new(signing_key, NULL /* no engine */); 168 if (ctx == NULL) 169 /* Error occurred */ 170 if (EVP_PKEY_sign_init(ctx) <= 0) 171 /* Error */ 172 if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) <= 0) 173 /* Error */ 174 if (EVP_PKEY_CTX_set_signature_md(ctx, EVP_sha256()) <= 0) 175 /* Error */ 176 177 /* Determine buffer length */ 178 if (EVP_PKEY_sign(ctx, NULL, &siglen, md, mdlen) <= 0) 179 /* Error */ 180 181 sig = OPENSSL_malloc(siglen); 182 183 if (sig == NULL) 184 /* malloc failure */ 185 186 if (EVP_PKEY_sign(ctx, sig, &siglen, md, mdlen) <= 0) 187 /* Error */ 188 189 /* Signature is siglen bytes written to buffer sig */ 190 191=head2 RSA-SHA256 with a pre-computed digest 192 193Sign a digest with RSA-SHA256 using one-shot functions. To be noted is that 194RSA-SHA256 is assumed to be an implementation of C<sha256WithRSAEncryption>, 195for which the padding is pre-determined to be B<RSA_PKCS1_PADDING>, and the 196input digest is assumed to have been computed using SHA256. 197 198 #include <openssl/evp.h> 199 #include <openssl/rsa.h> 200 201 EVP_PKEY_CTX *ctx; 202 /* md is a SHA-256 digest in this example. */ 203 unsigned char *md, *sig; 204 size_t mdlen = 32, siglen; 205 EVP_PKEY *signing_key; 206 207 /* 208 * NB: assumes signing_key and md are set up before the next 209 * step. signing_key must be an RSA private key and md must 210 * point to the SHA-256 digest to be signed. 211 */ 212 ctx = EVP_PKEY_CTX_new(signing_key, NULL /* no engine */); 213 alg = EVP_SIGNATURE_fetch(NULL, "RSA-SHA256", NULL); 214 215 if (ctx == NULL) 216 /* Error occurred */ 217 if (EVP_PKEY_sign_init_ex2(ctx, alg, NULL) <= 0) 218 /* Error */ 219 220 /* Determine buffer length */ 221 if (EVP_PKEY_sign(ctx, NULL, &siglen, md, mdlen) <= 0) 222 /* Error */ 223 224 sig = OPENSSL_malloc(siglen); 225 226 if (sig == NULL) 227 /* malloc failure */ 228 229 if (EVP_PKEY_sign(ctx, sig, &siglen, md, mdlen) <= 0) 230 /* Error */ 231 232 /* Signature is siglen bytes written to buffer sig */ 233 234 235=head2 RSA-SHA256, one-shot 236 237Sign a document with RSA-SHA256 using one-shot functions. 238To be noted is that RSA-SHA256 is assumed to be an implementation of 239C<sha256WithRSAEncryption>, for which the padding is pre-determined to be 240B<RSA_PKCS1_PADDING>. 241 242 #include <openssl/evp.h> 243 #include <openssl/rsa.h> 244 245 EVP_PKEY_CTX *ctx; 246 /* in is the input in this example. */ 247 unsigned char *in, *sig; 248 /* inlen is the length of the input in this example. */ 249 size_t inlen, siglen; 250 EVP_PKEY *signing_key; 251 EVP_SIGNATURE *alg; 252 253 /* 254 * NB: assumes signing_key, in and inlen are set up before 255 * the next step. signing_key must be an RSA private key, 256 * in must point to data to be digested and signed, and 257 * inlen must be the size of the data in bytes. 258 */ 259 ctx = EVP_PKEY_CTX_new(signing_key, NULL /* no engine */); 260 alg = EVP_SIGNATURE_fetch(NULL, "RSA-SHA256", NULL); 261 262 if (ctx == NULL || alg == NULL) 263 /* Error occurred */ 264 if (EVP_PKEY_sign_message_init(ctx, alg, NULL) <= 0) 265 /* Error */ 266 267 /* Determine sig buffer length */ 268 if (EVP_PKEY_sign(ctx, NULL, &siglen, in, inlen) <= 0) 269 /* Error */ 270 271 sig = OPENSSL_malloc(siglen); 272 273 if (sig == NULL) 274 /* malloc failure */ 275 276 if (EVP_PKEY_sign(ctx, sig, &siglen, in, inlen) <= 0) 277 /* Error */ 278 279 /* Signature is siglen bytes written to buffer sig */ 280 281 282=head2 RSA-SHA256, using update and final 283 284This is the same as the previous example, but allowing stream-like 285functionality. 286 287 #include <openssl/evp.h> 288 #include <openssl/rsa.h> 289 290 EVP_PKEY_CTX *ctx; 291 /* in is the input in this example. */ 292 unsigned char *in, *sig; 293 /* inlen is the length of the input in this example. */ 294 size_t inlen, siglen; 295 EVP_PKEY *signing_key; 296 EVP_SIGNATURE *alg; 297 298 /* 299 * NB: assumes signing_key, in and inlen are set up before 300 * the next step. signing_key must be an RSA private key, 301 * in must point to data to be digested and signed, and 302 * inlen must be the size of the data in bytes. 303 */ 304 ctx = EVP_PKEY_CTX_new(signing_key, NULL /* no engine */); 305 alg = EVP_SIGNATURE_fetch(NULL, "RSA-SHA256", NULL); 306 307 if (ctx == NULL || alg == NULL) 308 /* Error occurred */ 309 if (EVP_PKEY_sign_message_init(ctx, alg, NULL) <= 0) 310 /* Error */ 311 312 while (inlen > 0) { 313 if (EVP_PKEY_sign_message_update(ctx, in, inlen)) <= 0) 314 /* Error */ 315 if (inlen > 256) { 316 inlen -= 256; 317 in += 256; 318 } else { 319 inlen = 0; 320 } 321 } 322 323 /* Determine sig buffer length */ 324 if (EVP_PKEY_sign_message_final(ctx, NULL, &siglen) <= 0) 325 /* Error */ 326 327 sig = OPENSSL_malloc(siglen); 328 329 if (sig == NULL) 330 /* malloc failure */ 331 332 if (EVP_PKEY_sign_message_final(ctx, sig, &siglen) <= 0) 333 /* Error */ 334 335 /* Signature is siglen bytes written to buffer sig */ 336 337 338=head1 SEE ALSO 339 340L<EVP_PKEY_CTX_new(3)>, 341L<EVP_PKEY_CTX_ctrl(3)>, 342L<EVP_PKEY_encrypt(3)>, 343L<EVP_PKEY_decrypt(3)>, 344L<EVP_PKEY_verify(3)>, 345L<EVP_PKEY_verify_recover(3)>, 346L<EVP_PKEY_derive(3)> 347 348=head1 HISTORY 349 350The EVP_PKEY_sign_init() and EVP_PKEY_sign() functions were added in 351OpenSSL 1.0.0. 352 353The EVP_PKEY_sign_init_ex() function was added in OpenSSL 3.0. 354 355The EVP_PKEY_sign_init_ex2(), EVP_PKEY_sign_message_init(), 356EVP_PKEY_sign_message_update() and EVP_PKEY_sign_message_final() functions 357where added in OpenSSL 3.4. 358 359=head1 COPYRIGHT 360 361Copyright 2006-2024 The OpenSSL Project Authors. All Rights Reserved. 362 363Licensed under the Apache License 2.0 (the "License"). You may not use 364this file except in compliance with the License. You can obtain a copy 365in the file LICENSE in the source distribution or at 366L<https://www.openssl.org/source/license.html>. 367 368=cut 369
