_ Git - BearSSL/blob - inc/bearssl_ec.h

   1 /*
   2  * Copyright (c) 2016 Thomas Pornin <pornin@bolet.org>
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining
   5  * a copy of this software and associated documentation files (the
   6  * "Software"), to deal in the Software without restriction, including
   7  * without limitation the rights to use, copy, modify, merge, publish,
   8  * distribute, sublicense, and/or sell copies of the Software, and to
   9  * permit persons to whom the Software is furnished to do so, subject to
  10  * the following conditions:
  11  *
  12  * The above copyright notice and this permission notice shall be
  13  * included in all copies or substantial portions of the Software.
  14  *
  15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  16  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  17  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  18  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
  19  * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
  20  * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  21  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  22  * SOFTWARE.
  23  */
  24
  25 #ifndef BR_BEARSSL_EC_H__
  26 #define BR_BEARSSL_EC_H__
  27
  28 #include <stddef.h>
  29 #include <stdint.h>
  30
  31 #include "bearssl_rand.h"
  32
  33 #ifdef __cplusplus
  34 extern "C" {
  35 #endif
  36
  37 /** \file bearssl_ec.h
  38  *
  39  * # Elliptic Curves
  40  *
  41  * This file documents the EC implementations provided with BearSSL, and
  42  * ECDSA.
  43  *
  44  * ## Elliptic Curve API
  45  *
  46  * Only "named curves" are supported. Each EC implementation supports
  47  * one or several named curves, identified by symbolic identifiers.
  48  * These identifiers are small integers, that correspond to the values
  49  * registered by the
  50  * [IANA](http://www.iana.org/assignments/tls-parameters/tls-parameters.xhtml#tls-parameters-8).
  51  *
  52  * Since all currently defined elliptic curve identifiers are in the 0..31
  53  * range, it is convenient to encode support of some curves in a 32-bit
  54  * word, such that bit x corresponds to curve of identifier x.
  55  *
  56  * An EC implementation is incarnated by a `br_ec_impl` instance, that
  57  * offers the following fields:
  58  *
  59  *   - `supported_curves`
  60  *
  61  *      A 32-bit word that documents the identifiers of the curves supported
  62  *      by this implementation.
  63  *
  64  *   - `generator()`
  65  *
  66  *      Callback method that returns a pointer to the conventional generator
  67  *      point for that curve.
  68  *
  69  *   - `order()`
  70  *
  71  *      Callback method that returns a pointer to the subgroup order for
  72  *      that curve. That value uses unsigned big-endian encoding.
  73  *
  74  *   - `xoff()`
  75  *
  76  *      Callback method that returns the offset and length of the X
  77  *      coordinate in an encoded point.
  78  *
  79  *   - `mul()`
  80  *
  81  *      Multiply a curve point with an integer.
  82  *
  83  *   - `mulgen()`
  84  *
  85  *      Multiply the curve generator with an integer. This may be faster
  86  *      than the generic `mul()`.
  87  *
  88  *   - `muladd()`
  89  *
  90  *      Multiply two curve points by two integers, and return the sum of
  91  *      the two products.
  92  *
  93  * All curve points are represented in uncompressed format. The `mul()`
  94  * and `muladd()` methods take care to validate that the provided points
  95  * are really part of the relevant curve subgroup.
  96  *
  97  * For all point multiplication functions, the following holds:
  98  *
  99  *   - Functions validate that the provided points are valid members
 100  *     of the relevant curve subgroup. An error is reported if that is
 101  *     not the case.
 102  *
 103  *   - Processing is constant-time, even if the point operands are not
 104  *     valid. This holds for both the source and resulting points, and
 105  *     the multipliers (integers). Only the byte length of the provided
 106  *     multiplier arrays (not their actual value length in bits) may
 107  *     leak through timing-based side channels.
 108  *
 109  *   - The multipliers (integers) MUST be lower than the subgroup order.
 110  *     If this property is not met, then the result is indeterminate,
 111  *     but an error value is not ncessearily returned.
 112  *
 113  *
 114  * ## ECDSA
 115  *
 116  * ECDSA signatures have two standard formats, called "raw" and "asn1".
 117  * Internally, such a signature is a pair of modular integers `(r,s)`.
 118  * The "raw" format is the concatenation of the unsigned big-endian
 119  * encodings of these two integers, possibly left-padded with zeros so
 120  * that they have the same encoded length. The "asn1" format is the
 121  * DER encoding of an ASN.1 structure that contains the two integer
 122  * values:
 123  *
 124  *     ECDSASignature ::= SEQUENCE {
 125  *         r   INTEGER,
 126  *         s   INTEGER
 127  *     }
 128  *
 129  * In general, in all of X.509 and SSL/TLS, the "asn1" format is used.
 130  * BearSSL offers ECDSA implementations for both formats; conversion
 131  * functions between the two formats are also provided. Conversion of a
 132  * "raw" format signature into "asn1" may enlarge a signature by no more
 133  * than 9 bytes for all supported curves; conversely, conversion of an
 134  * "asn1" signature to "raw" may expand the signature but the "raw"
 135  * length will never be more than twice the length of the "asn1" length
 136  * (and usually it will be shorter).
 137  *
 138  * Note that for a given signature, the "raw" format is not fully
 139  * deterministic, in that it does not enforce a minimal common length.
 140  */
 141
 142 /*
 143  * Standard curve ID. These ID are equal to the assigned numerical
 144  * identifiers assigned to these curves for TLS:
 145  *    http://www.iana.org/assignments/tls-parameters/tls-parameters.xhtml#tls-parameters-8
 146  */
 147
 148 /** \brief Identifier for named curve sect163k1. */
 149 #define BR_EC_sect163k1           1
 150
 151 /** \brief Identifier for named curve sect163r1. */
 152 #define BR_EC_sect163r1           2
 153
 154 /** \brief Identifier for named curve sect163r2. */
 155 #define BR_EC_sect163r2           3
 156
 157 /** \brief Identifier for named curve sect193r1. */
 158 #define BR_EC_sect193r1           4
 159
 160 /** \brief Identifier for named curve sect193r2. */
 161 #define BR_EC_sect193r2           5
 162
 163 /** \brief Identifier for named curve sect233k1. */
 164 #define BR_EC_sect233k1           6
 165
 166 /** \brief Identifier for named curve sect233r1. */
 167 #define BR_EC_sect233r1           7
 168
 169 /** \brief Identifier for named curve sect239k1. */
 170 #define BR_EC_sect239k1           8
 171
 172 /** \brief Identifier for named curve sect283k1. */
 173 #define BR_EC_sect283k1           9
 174
 175 /** \brief Identifier for named curve sect283r1. */
 176 #define BR_EC_sect283r1          10
 177
 178 /** \brief Identifier for named curve sect409k1. */
 179 #define BR_EC_sect409k1          11
 180
 181 /** \brief Identifier for named curve sect409r1. */
 182 #define BR_EC_sect409r1          12
 183
 184 /** \brief Identifier for named curve sect571k1. */
 185 #define BR_EC_sect571k1          13
 186
 187 /** \brief Identifier for named curve sect571r1. */
 188 #define BR_EC_sect571r1          14
 189
 190 /** \brief Identifier for named curve secp160k1. */
 191 #define BR_EC_secp160k1          15
 192
 193 /** \brief Identifier for named curve secp160r1. */
 194 #define BR_EC_secp160r1          16
 195
 196 /** \brief Identifier for named curve secp160r2. */
 197 #define BR_EC_secp160r2          17
 198
 199 /** \brief Identifier for named curve secp192k1. */
 200 #define BR_EC_secp192k1          18
 201
 202 /** \brief Identifier for named curve secp192r1. */
 203 #define BR_EC_secp192r1          19
 204
 205 /** \brief Identifier for named curve secp224k1. */
 206 #define BR_EC_secp224k1          20
 207
 208 /** \brief Identifier for named curve secp224r1. */
 209 #define BR_EC_secp224r1          21
 210
 211 /** \brief Identifier for named curve secp256k1. */
 212 #define BR_EC_secp256k1          22
 213
 214 /** \brief Identifier for named curve secp256r1. */
 215 #define BR_EC_secp256r1          23
 216
 217 /** \brief Identifier for named curve secp384r1. */
 218 #define BR_EC_secp384r1          24
 219
 220 /** \brief Identifier for named curve secp521r1. */
 221 #define BR_EC_secp521r1          25
 222
 223 /** \brief Identifier for named curve brainpoolP256r1. */
 224 #define BR_EC_brainpoolP256r1    26
 225
 226 /** \brief Identifier for named curve brainpoolP384r1. */
 227 #define BR_EC_brainpoolP384r1    27
 228
 229 /** \brief Identifier for named curve brainpoolP512r1. */
 230 #define BR_EC_brainpoolP512r1    28
 231
 232 /** \brief Identifier for named curve Curve25519. */
 233 #define BR_EC_curve25519         29
 234
 235 /** \brief Identifier for named curve Curve448. */
 236 #define BR_EC_curve448           30
 237
 238 /**
 239  * \brief Structure for an EC public key.
 240  */
 241 typedef struct {
 242         /** \brief Identifier for the curve used by this key. */
 243         int curve;
 244         /** \brief Public curve point (uncompressed format). */
 245         unsigned char *q;
 246         /** \brief Length of public curve point (in bytes). */
 247         size_t qlen;
 248 } br_ec_public_key;
 249
 250 /**
 251  * \brief Structure for an EC private key.
 252  *
 253  * The private key is an integer modulo the curve subgroup order. The
 254  * encoding below tolerates extra leading zeros. In general, it is
 255  * recommended that the private key has the same length as the curve
 256  * subgroup order.
 257  */
 258 typedef struct {
 259         /** \brief Identifier for the curve used by this key. */
 260         int curve;
 261         /** \brief Private key (integer, unsigned big-endian encoding). */
 262         unsigned char *x;
 263         /** \brief Private key length (in bytes). */
 264         size_t xlen;
 265 } br_ec_private_key;
 266
 267 /**
 268  * \brief Type for an EC implementation.
 269  */
 270 typedef struct {
 271         /**
 272          * \brief Supported curves.
 273          *
 274          * This word is a bitfield: bit `x` is set if the curve of ID `x`
 275          * is supported. E.g. an implementation supporting both NIST P-256
 276          * (secp256r1, ID 23) and NIST P-384 (secp384r1, ID 24) will have
 277          * value `0x01800000` in this field.
 278          */
 279         uint32_t supported_curves;
 280
 281         /**
 282          * \brief Get the conventional generator.
 283          *
 284          * This function returns the conventional generator (encoded
 285          * curve point) for the specified curve. This function MUST NOT
 286          * be called if the curve is not supported.
 287          *
 288          * \param curve   curve identifier.
 289          * \param len     receiver for the encoded generator length (in bytes).
 290          * \return  the encoded generator.
 291          */
 292         const unsigned char *(*generator)(int curve, size_t *len);
 293
 294         /**
 295          * \brief Get the subgroup order.
 296          *
 297          * This function returns the order of the subgroup generated by
 298          * the conventional generator, for the specified curve. Unsigned
 299          * big-endian encoding is used. This function MUST NOT be called
 300          * if the curve is not supported.
 301          *
 302          * \param curve   curve identifier.
 303          * \param len     receiver for the encoded order length (in bytes).
 304          * \return  the encoded order.
 305          */
 306         const unsigned char *(*order)(int curve, size_t *len);
 307
 308         /**
 309          * \brief Get the offset and length for the X coordinate.
 310          *
 311          * This function returns the offset and length (in bytes) of
 312          * the X coordinate in an encoded non-zero point.
 313          *
 314          * \param curve   curve identifier.
 315          * \param len     receiver for the X coordinate length (in bytes).
 316          * \return  the offset for the X coordinate (in bytes).
 317          */
 318         size_t (*xoff)(int curve, size_t *len);
 319
 320         /**
 321          * \brief Multiply a curve point by an integer.
 322          *
 323          * The source point is provided in array `G` (of size `Glen` bytes);
 324          * the multiplication result is written over it. The multiplier
 325          * `x` (of size `xlen` bytes) uses unsigned big-endian encoding.
 326          *
 327          * Rules:
 328          *
 329          *   - The specified curve MUST be supported.
 330          *
 331          *   - The source point must be a valid point on the relevant curve
 332          *     subgroup (and not the "point at infinity" either). If this is
 333          *     not the case, then this function returns an error (0).
 334          *
 335          *   - The multiplier integer MUST be non-zero and less than the
 336          *     curve subgroup order. If this property does not hold, then
 337          *     the result is indeterminate and an error code is not
 338          *     guaranteed.
 339          *
 340          * Returned value is 1 on success, 0 on error. On error, the
 341          * contents of `G` are indeterminate.
 342          *
 343          * \param G       point to multiply.
 344          * \param Glen    length of the encoded point (in bytes).
 345          * \param x       multiplier (unsigned big-endian).
 346          * \param xlen    multiplier length (in bytes).
 347          * \param curve   curve identifier.
 348          * \return  1 on success, 0 on error.
 349          */
 350         uint32_t (*mul)(unsigned char *G, size_t Glen,
 351                 const unsigned char *x, size_t xlen, int curve);
 352
 353         /**
 354          * \brief Multiply the generator by an integer.
 355          *
 356          * The multiplier MUST be non-zero and less than the curve
 357          * subgroup order. Results are indeterminate if this property
 358          * does not hold.
 359          *
 360          * \param R       output buffer for the point.
 361          * \param x       multiplier (unsigned big-endian).
 362          * \param xlen    multiplier length (in bytes).
 363          * \param curve   curve identifier.
 364          * \return  encoded result point length (in bytes).
 365          */
 366         size_t (*mulgen)(unsigned char *R,
 367                 const unsigned char *x, size_t xlen, int curve);
 368
 369         /**
 370          * \brief Multiply two points by two integers and add the
 371          * results.
 372          *
 373          * The point `x*A + y*B` is computed and written back in the `A`
 374          * array.
 375          *
 376          * Rules:
 377          *
 378          *   - The specified curve MUST be supported.
 379          *
 380          *   - The source points (`A` and `B`)  must be valid points on
 381          *     the relevant curve subgroup (and not the "point at
 382          *     infinity" either). If this is not the case, then this
 383          *     function returns an error (0).
 384          *
 385          *   - If the `B` pointer is `NULL`, then the conventional
 386          *     subgroup generator is used. With some implementations,
 387          *     this may be faster than providing a pointer to the
 388          *     generator.
 389          *
 390          *   - The multiplier integers (`x` and `y`) MUST be non-zero
 391          *     and less than the curve subgroup order. If either integer
 392          *     is zero, then an error is reported, but if one of them is
 393          *     not lower than the subgroup order, then the result is
 394          *     indeterminate and an error code is not guaranteed.
 395          *
 396          *   - If the final result is the point at infinity, then an
 397          *     error is returned.
 398          *
 399          * Returned value is 1 on success, 0 on error. On error, the
 400          * contents of `A` are indeterminate.
 401          *
 402          * \param A       first point to multiply.
 403          * \param B       second point to multiply (`NULL` for the generator).
 404          * \param len     common length of the encoded points (in bytes).
 405          * \param x       multiplier for `A` (unsigned big-endian).
 406          * \param xlen    length of multiplier for `A` (in bytes).
 407          * \param y       multiplier for `A` (unsigned big-endian).
 408          * \param ylen    length of multiplier for `A` (in bytes).
 409          * \param curve   curve identifier.
 410          * \return  1 on success, 0 on error.
 411          */
 412         uint32_t (*muladd)(unsigned char *A, const unsigned char *B, size_t len,
 413                 const unsigned char *x, size_t xlen,
 414                 const unsigned char *y, size_t ylen, int curve);
 415 } br_ec_impl;
 416
 417 /**
 418  * \brief EC implementation "i31".
 419  *
 420  * This implementation internally uses generic code for modular integers,
 421  * with a representation as sequences of 31-bit words. It supports secp256r1,
 422  * secp384r1 and secp521r1 (aka NIST curves P-256, P-384 and P-521).
 423  */
 424 extern const br_ec_impl br_ec_prime_i31;
 425
 426 /**
 427  * \brief EC implementation "i15".
 428  *
 429  * This implementation internally uses generic code for modular integers,
 430  * with a representation as sequences of 15-bit words. It supports secp256r1,
 431  * secp384r1 and secp521r1 (aka NIST curves P-256, P-384 and P-521).
 432  */
 433 extern const br_ec_impl br_ec_prime_i15;
 434
 435 /**
 436  * \brief EC implementation "m15" for P-256.
 437  *
 438  * This implementation uses specialised code for curve secp256r1 (also
 439  * known as NIST P-256), with optional Karatsuba decomposition, and fast
 440  * modular reduction thanks to the field modulus special format. Only
 441  * 32-bit multiplications are used (with 32-bit results, not 64-bit).
 442  */
 443 extern const br_ec_impl br_ec_p256_m15;
 444
 445 /**
 446  * \brief EC implementation "m31" for P-256.
 447  *
 448  * This implementation uses specialised code for curve secp256r1 (also
 449  * known as NIST P-256), relying on multiplications of 31-bit values
 450  * (MUL31).
 451  */
 452 extern const br_ec_impl br_ec_p256_m31;
 453
 454 /**
 455  * \brief EC implementation "i15" (generic code) for Curve25519.
 456  *
 457  * This implementation uses the generic code for modular integers (with
 458  * 15-bit words) to support Curve25519. Due to the specificities of the
 459  * curve definition, the following applies:
 460  *
 461  *   - `muladd()` is not implemented (the function returns 0 systematically).
 462  *   - `order()` returns 2^255-1, since the point multiplication algorithm
 463  *     accepts any 32-bit integer as input (it clears the top bit and low
 464  *     three bits systematically).
 465  */
 466 extern const br_ec_impl br_ec_c25519_i15;
 467
 468 /**
 469  * \brief EC implementation "i31" (generic code) for Curve25519.
 470  *
 471  * This implementation uses the generic code for modular integers (with
 472  * 31-bit words) to support Curve25519. Due to the specificities of the
 473  * curve definition, the following applies:
 474  *
 475  *   - `muladd()` is not implemented (the function returns 0 systematically).
 476  *   - `order()` returns 2^255-1, since the point multiplication algorithm
 477  *     accepts any 32-bit integer as input (it clears the top bit and low
 478  *     three bits systematically).
 479  */
 480 extern const br_ec_impl br_ec_c25519_i31;
 481
 482 /**
 483  * \brief EC implementation "m15" (specialised code) for Curve25519.
 484  *
 485  * This implementation uses custom code relying on multiplication of
 486  * integers up to 15 bits. Due to the specificities of the curve
 487  * definition, the following applies:
 488  *
 489  *   - `muladd()` is not implemented (the function returns 0 systematically).
 490  *   - `order()` returns 2^255-1, since the point multiplication algorithm
 491  *     accepts any 32-bit integer as input (it clears the top bit and low
 492  *     three bits systematically).
 493  */
 494 extern const br_ec_impl br_ec_c25519_m15;
 495
 496 /**
 497  * \brief EC implementation "m31" (specialised code) for Curve25519.
 498  *
 499  * This implementation uses custom code relying on multiplication of
 500  * integers up to 31 bits. Due to the specificities of the curve
 501  * definition, the following applies:
 502  *
 503  *   - `muladd()` is not implemented (the function returns 0 systematically).
 504  *   - `order()` returns 2^255-1, since the point multiplication algorithm
 505  *     accepts any 32-bit integer as input (it clears the top bit and low
 506  *     three bits systematically).
 507  */
 508 extern const br_ec_impl br_ec_c25519_m31;
 509
 510 /**
 511  * \brief EC implementation "m62" (specialised code) for Curve25519.
 512  *
 513  * This implementation uses custom code relying on multiplication of
 514  * integers up to 62 bits, with a 124-bit result. This implementation is
 515  * defined only on platforms that offer the 64x64->128 multiplication
 516  * support; use `br_ec_c25519_m62_get()` to dynamically obtain a pointer
 517  * to that implementation. Due to the specificities of the curve
 518  * definition, the following applies:
 519  *
 520  *   - `muladd()` is not implemented (the function returns 0 systematically).
 521  *   - `order()` returns 2^255-1, since the point multiplication algorithm
 522  *     accepts any 32-bit integer as input (it clears the top bit and low
 523  *     three bits systematically).
 524  */
 525 extern const br_ec_impl br_ec_c25519_m62;
 526
 527 /**
 528  * \brief Get the "m62" implementation of Curve25519, if available.
 529  *
 530  * \return  the implementation, or 0.
 531  */
 532 const br_ec_impl *br_ec_c25519_m62_get(void);
 533
 534 /**
 535  * \brief Aggregate EC implementation "m15".
 536  *
 537  * This implementation is a wrapper for:
 538  *
 539  *   - `br_ec_c25519_m15` for Curve25519
 540  *   - `br_ec_p256_m15` for NIST P-256
 541  *   - `br_ec_prime_i15` for other curves (NIST P-384 and NIST-P512)
 542  */
 543 extern const br_ec_impl br_ec_all_m15;
 544
 545 /**
 546  * \brief Aggregate EC implementation "m31".
 547  *
 548  * This implementation is a wrapper for:
 549  *
 550  *   - `br_ec_c25519_m31` for Curve25519
 551  *   - `br_ec_p256_m31` for NIST P-256
 552  *   - `br_ec_prime_i31` for other curves (NIST P-384 and NIST-P512)
 553  */
 554 extern const br_ec_impl br_ec_all_m31;
 555
 556 /**
 557  * \brief Get the "default" EC implementation for the current system.
 558  *
 559  * This returns a pointer to the preferred implementation on the
 560  * current system.
 561  *
 562  * \return  the default EC implementation.
 563  */
 564 const br_ec_impl *br_ec_get_default(void);
 565
 566 /**
 567  * \brief Convert a signature from "raw" to "asn1".
 568  *
 569  * Conversion is done "in place" and the new length is returned.
 570  * Conversion may enlarge the signature, but by no more than 9 bytes at
 571  * most. On error, 0 is returned (error conditions include an odd raw
 572  * signature length, or an oversized integer).
 573  *
 574  * \param sig       signature to convert.
 575  * \param sig_len   signature length (in bytes).
 576  * \return  the new signature length, or 0 on error.
 577  */
 578 size_t br_ecdsa_raw_to_asn1(void *sig, size_t sig_len);
 579
 580 /**
 581  * \brief Convert a signature from "asn1" to "raw".
 582  *
 583  * Conversion is done "in place" and the new length is returned.
 584  * Conversion may enlarge the signature, but the new signature length
 585  * will be less than twice the source length at most. On error, 0 is
 586  * returned (error conditions include an invalid ASN.1 structure or an
 587  * oversized integer).
 588  *
 589  * \param sig       signature to convert.
 590  * \param sig_len   signature length (in bytes).
 591  * \return  the new signature length, or 0 on error.
 592  */
 593 size_t br_ecdsa_asn1_to_raw(void *sig, size_t sig_len);
 594
 595 /**
 596  * \brief Type for an ECDSA signer function.
 597  *
 598  * A pointer to the EC implementation is provided. The hash value is
 599  * assumed to have the length inferred from the designated hash function
 600  * class.
 601  *
 602  * Signature is written in the buffer pointed to by `sig`, and the length
 603  * (in bytes) is returned. On error, nothing is written in the buffer,
 604  * and 0 is returned. This function returns 0 if the specified curve is
 605  * not supported by the provided EC implementation.
 606  *
 607  * The signature format is either "raw" or "asn1", depending on the
 608  * implementation; maximum length is predictable from the implemented
 609  * curve:
 610  *
 611  * | curve      | raw | asn1 |
 612  * | :--------- | --: | ---: |
 613  * | NIST P-256 |  64 |   72 |
 614  * | NIST P-384 |  96 |  104 |
 615  * | NIST P-521 | 132 |  139 |
 616  *
 617  * \param impl         EC implementation to use.
 618  * \param hf           hash function used to process the data.
 619  * \param hash_value   signed data (hashed).
 620  * \param sk           EC private key.
 621  * \param sig          destination buffer.
 622  * \return  the signature length (in bytes), or 0 on error.
 623  */
 624 typedef size_t (*br_ecdsa_sign)(const br_ec_impl *impl,
 625         const br_hash_class *hf, const void *hash_value,
 626         const br_ec_private_key *sk, void *sig);
 627
 628 /**
 629  * \brief Type for an ECDSA signature verification function.
 630  *
 631  * A pointer to the EC implementation is provided. The hashed value,
 632  * computed over the purportedly signed data, is also provided with
 633  * its length.
 634  *
 635  * The signature format is either "raw" or "asn1", depending on the
 636  * implementation.
 637  *
 638  * Returned value is 1 on success (valid signature), 0 on error. This
 639  * function returns 0 if the specified curve is not supported by the
 640  * provided EC implementation.
 641  *
 642  * \param impl       EC implementation to use.
 643  * \param hash       signed data (hashed).
 644  * \param hash_len   hash value length (in bytes).
 645  * \param pk         EC public key.
 646  * \param sig        signature.
 647  * \param sig_len    signature length (in bytes).
 648  * \return  1 on success, 0 on error.
 649  */
 650 typedef uint32_t (*br_ecdsa_vrfy)(const br_ec_impl *impl,
 651         const void *hash, size_t hash_len,
 652         const br_ec_public_key *pk, const void *sig, size_t sig_len);
 653
 654 /**
 655  * \brief ECDSA signature generator, "i31" implementation, "asn1" format.
 656  *
 657  * \see br_ecdsa_sign()
 658  *
 659  * \param impl         EC implementation to use.
 660  * \param hf           hash function used to process the data.
 661  * \param hash_value   signed data (hashed).
 662  * \param sk           EC private key.
 663  * \param sig          destination buffer.
 664  * \return  the signature length (in bytes), or 0 on error.
 665  */
 666 size_t br_ecdsa_i31_sign_asn1(const br_ec_impl *impl,
 667         const br_hash_class *hf, const void *hash_value,
 668         const br_ec_private_key *sk, void *sig);
 669
 670 /**
 671  * \brief ECDSA signature generator, "i31" implementation, "raw" format.
 672  *
 673  * \see br_ecdsa_sign()
 674  *
 675  * \param impl         EC implementation to use.
 676  * \param hf           hash function used to process the data.
 677  * \param hash_value   signed data (hashed).
 678  * \param sk           EC private key.
 679  * \param sig          destination buffer.
 680  * \return  the signature length (in bytes), or 0 on error.
 681  */
 682 size_t br_ecdsa_i31_sign_raw(const br_ec_impl *impl,
 683         const br_hash_class *hf, const void *hash_value,
 684         const br_ec_private_key *sk, void *sig);
 685
 686 /**
 687  * \brief ECDSA signature verifier, "i31" implementation, "asn1" format.
 688  *
 689  * \see br_ecdsa_vrfy()
 690  *
 691  * \param impl       EC implementation to use.
 692  * \param hash       signed data (hashed).
 693  * \param hash_len   hash value length (in bytes).
 694  * \param pk         EC public key.
 695  * \param sig        signature.
 696  * \param sig_len    signature length (in bytes).
 697  * \return  1 on success, 0 on error.
 698  */
 699 uint32_t br_ecdsa_i31_vrfy_asn1(const br_ec_impl *impl,
 700         const void *hash, size_t hash_len,
 701         const br_ec_public_key *pk, const void *sig, size_t sig_len);
 702
 703 /**
 704  * \brief ECDSA signature verifier, "i31" implementation, "raw" format.
 705  *
 706  * \see br_ecdsa_vrfy()
 707  *
 708  * \param impl       EC implementation to use.
 709  * \param hash       signed data (hashed).
 710  * \param hash_len   hash value length (in bytes).
 711  * \param pk         EC public key.
 712  * \param sig        signature.
 713  * \param sig_len    signature length (in bytes).
 714  * \return  1 on success, 0 on error.
 715  */
 716 uint32_t br_ecdsa_i31_vrfy_raw(const br_ec_impl *impl,
 717         const void *hash, size_t hash_len,
 718         const br_ec_public_key *pk, const void *sig, size_t sig_len);
 719
 720 /**
 721  * \brief ECDSA signature generator, "i15" implementation, "asn1" format.
 722  *
 723  * \see br_ecdsa_sign()
 724  *
 725  * \param impl         EC implementation to use.
 726  * \param hf           hash function used to process the data.
 727  * \param hash_value   signed data (hashed).
 728  * \param sk           EC private key.
 729  * \param sig          destination buffer.
 730  * \return  the signature length (in bytes), or 0 on error.
 731  */
 732 size_t br_ecdsa_i15_sign_asn1(const br_ec_impl *impl,
 733         const br_hash_class *hf, const void *hash_value,
 734         const br_ec_private_key *sk, void *sig);
 735
 736 /**
 737  * \brief ECDSA signature generator, "i15" implementation, "raw" format.
 738  *
 739  * \see br_ecdsa_sign()
 740  *
 741  * \param impl         EC implementation to use.
 742  * \param hf           hash function used to process the data.
 743  * \param hash_value   signed data (hashed).
 744  * \param sk           EC private key.
 745  * \param sig          destination buffer.
 746  * \return  the signature length (in bytes), or 0 on error.
 747  */
 748 size_t br_ecdsa_i15_sign_raw(const br_ec_impl *impl,
 749         const br_hash_class *hf, const void *hash_value,
 750         const br_ec_private_key *sk, void *sig);
 751
 752 /**
 753  * \brief ECDSA signature verifier, "i15" implementation, "asn1" format.
 754  *
 755  * \see br_ecdsa_vrfy()
 756  *
 757  * \param impl       EC implementation to use.
 758  * \param hash       signed data (hashed).
 759  * \param hash_len   hash value length (in bytes).
 760  * \param pk         EC public key.
 761  * \param sig        signature.
 762  * \param sig_len    signature length (in bytes).
 763  * \return  1 on success, 0 on error.
 764  */
 765 uint32_t br_ecdsa_i15_vrfy_asn1(const br_ec_impl *impl,
 766         const void *hash, size_t hash_len,
 767         const br_ec_public_key *pk, const void *sig, size_t sig_len);
 768
 769 /**
 770  * \brief ECDSA signature verifier, "i15" implementation, "raw" format.
 771  *
 772  * \see br_ecdsa_vrfy()
 773  *
 774  * \param impl       EC implementation to use.
 775  * \param hash       signed data (hashed).
 776  * \param hash_len   hash value length (in bytes).
 777  * \param pk         EC public key.
 778  * \param sig        signature.
 779  * \param sig_len    signature length (in bytes).
 780  * \return  1 on success, 0 on error.
 781  */
 782 uint32_t br_ecdsa_i15_vrfy_raw(const br_ec_impl *impl,
 783         const void *hash, size_t hash_len,
 784         const br_ec_public_key *pk, const void *sig, size_t sig_len);
 785
 786 /**
 787  * \brief Get "default" ECDSA implementation (signer, asn1 format).
 788  *
 789  * This returns the preferred implementation of ECDSA signature generation
 790  * ("asn1" output format) on the current system.
 791  *
 792  * \return  the default implementation.
 793  */
 794 br_ecdsa_sign br_ecdsa_sign_asn1_get_default(void);
 795
 796 /**
 797  * \brief Get "default" ECDSA implementation (signer, raw format).
 798  *
 799  * This returns the preferred implementation of ECDSA signature generation
 800  * ("raw" output format) on the current system.
 801  *
 802  * \return  the default implementation.
 803  */
 804 br_ecdsa_sign br_ecdsa_sign_raw_get_default(void);
 805
 806 /**
 807  * \brief Get "default" ECDSA implementation (verifier, asn1 format).
 808  *
 809  * This returns the preferred implementation of ECDSA signature verification
 810  * ("asn1" output format) on the current system.
 811  *
 812  * \return  the default implementation.
 813  */
 814 br_ecdsa_vrfy br_ecdsa_vrfy_asn1_get_default(void);
 815
 816 /**
 817  * \brief Get "default" ECDSA implementation (verifier, raw format).
 818  *
 819  * This returns the preferred implementation of ECDSA signature verification
 820  * ("raw" output format) on the current system.
 821  *
 822  * \return  the default implementation.
 823  */
 824 br_ecdsa_vrfy br_ecdsa_vrfy_raw_get_default(void);
 825
 826 /**
 827  * \brief Maximum size for EC private key element buffer.
 828  *
 829  * This is the largest number of bytes that `br_ec_keygen()` may need or
 830  * ever return.
 831  */
 832 #define BR_EC_KBUF_PRIV_MAX_SIZE   72
 833
 834 /**
 835  * \brief Maximum size for EC public key element buffer.
 836  *
 837  * This is the largest number of bytes that `br_ec_compute_public()` may
 838  * need or ever return.
 839  */
 840 #define BR_EC_KBUF_PUB_MAX_SIZE    145
 841
 842 /**
 843  * \brief Generate a new EC private key.
 844  *
 845  * If the specified `curve` is not supported by the elliptic curve
 846  * implementation (`impl`), then this function returns zero.
 847  *
 848  * The `sk` structure fields are set to the new private key data. In
 849  * particular, `sk.x` is made to point to the provided key buffer (`kbuf`),
 850  * in which the actual private key data is written. That buffer is assumed
 851  * to be large enough. The `BR_EC_KBUF_PRIV_MAX_SIZE` defines the maximum
 852  * size for all supported curves.
 853  *
 854  * The number of bytes used in `kbuf` is returned. If `kbuf` is `NULL`, then
 855  * the private key is not actually generated, and `sk` may also be `NULL`;
 856  * the minimum length for `kbuf` is still computed and returned.
 857  *
 858  * If `sk` is `NULL` but `kbuf` is not `NULL`, then the private key is
 859  * still generated and stored in `kbuf`.
 860  *
 861  * \param rng_ctx   source PRNG context (already initialized).
 862  * \param impl      the elliptic curve implementation.
 863  * \param sk        the private key structure to fill, or `NULL`.
 864  * \param kbuf      the key element buffer, or `NULL`.
 865  * \param curve     the curve identifier.
 866  * \return  the key data length (in bytes), or zero.
 867  */
 868 size_t br_ec_keygen(const br_prng_class **rng_ctx,
 869         const br_ec_impl *impl, br_ec_private_key *sk,
 870         void *kbuf, int curve);
 871
 872 /**
 873  * \brief Compute EC public key from EC private key.
 874  *
 875  * This function uses the provided elliptic curve implementation (`impl`)
 876  * to compute the public key corresponding to the private key held in `sk`.
 877  * The public key point is written into `kbuf`, which is then linked from
 878  * the `*pk` structure. The size of the public key point, i.e. the number
 879  * of bytes used in `kbuf`, is returned.
 880  *
 881  * If `kbuf` is `NULL`, then the public key point is NOT computed, and
 882  * the public key structure `*pk` is unmodified (`pk` may be `NULL` in
 883  * that case). The size of the public key point is still returned.
 884  *
 885  * If `pk` is `NULL` but `kbuf` is not `NULL`, then the public key
 886  * point is computed and stored in `kbuf`, and its size is returned.
 887  *
 888  * If the curve used by the private key is not supported by the curve
 889  * implementation, then this function returns zero.
 890  *
 891  * The private key MUST be valid. An off-range private key value is not
 892  * necessarily detected, and leads to unpredictable results.
 893  *
 894  * \param impl   the elliptic curve implementation.
 895  * \param pk     the public key structure to fill (or `NULL`).
 896  * \param kbuf   the public key point buffer (or `NULL`).
 897  * \param sk     the source private key.
 898  * \return  the public key point length (in bytes), or zero.
 899  */
 900 size_t br_ec_compute_pub(const br_ec_impl *impl, br_ec_public_key *pk,
 901         void *kbuf, const br_ec_private_key *sk);
 902
 903 #ifdef __cplusplus
 904 }
 905 #endif
 906
 907 #endif