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 #include "inner.h" 26 27 /* see bearssl_ec.h */ 28 size_t 29 br_ecdsa_asn1_to_raw(void *sig, size_t sig_len) 30 { 31 /* 32 * Note: this code is a bit lenient in that it accepts a few 33 * deviations to DER with regards to minimality of encoding of 34 * lengths and integer values. These deviations are still 35 * unambiguous. 36 * 37 * Signature format is a SEQUENCE of two INTEGER values. We 38 * support only integers of less than 127 bytes each (signed 39 * encoding) so the resulting raw signature will have length 40 * at most 254 bytes. 41 */ 42 43 unsigned char *buf, *r, *s; 44 size_t zlen, rlen, slen, off; 45 unsigned char tmp[254]; 46 47 buf = sig; 48 if (sig_len < 8) { 49 return 0; 50 } 51 52 /* 53 * First byte is SEQUENCE tag. 54 */ 55 if (buf[0] != 0x30) { 56 return 0; 57 } 58 59 /* 60 * The SEQUENCE length will be encoded over one or two bytes. We 61 * limit the total SEQUENCE contents to 255 bytes, because it 62 * makes things simpler; this is enough for subgroup orders up 63 * to 999 bits. 64 */ 65 zlen = buf[1]; 66 if (zlen > 0x80) { 67 if (zlen != 0x81) { 68 return 0; 69 } 70 zlen = buf[2]; 71 if (zlen != sig_len - 3) { 72 return 0; 73 } 74 off = 3; 75 } else { 76 if (zlen != sig_len - 2) { 77 return 0; 78 } 79 off = 2; 80 } 81 82 /* 83 * First INTEGER (r). 84 */ 85 if (buf[off ++] != 0x02) { 86 return 0; 87 } 88 rlen = buf[off ++]; 89 if (rlen >= 0x80) { 90 return 0; 91 } 92 r = buf + off; 93 off += rlen; 94 95 /* 96 * Second INTEGER (s). 97 */ 98 if (off + 2 > sig_len) { 99 return 0; 100 } 101 if (buf[off ++] != 0x02) { 102 return 0; 103 } 104 slen = buf[off ++]; 105 if (slen >= 0x80 || slen != sig_len - off) { 106 return 0; 107 } 108 s = buf + off; 109 110 /* 111 * Removing leading zeros from r and s. 112 */ 113 while (rlen > 0 && *r == 0) { 114 rlen --; 115 r ++; 116 } 117 while (slen > 0 && *s == 0) { 118 slen --; 119 s ++; 120 } 121 122 /* 123 * Compute common length for the two integers, then copy integers 124 * into the temporary buffer, and finally copy it back over the 125 * signature buffer. 126 */ 127 zlen = rlen > slen ? rlen : slen; 128 sig_len = zlen << 1; 129 memset(tmp, 0, sig_len); 130 memcpy(tmp + zlen - rlen, r, rlen); 131 memcpy(tmp + sig_len - slen, s, slen); 132 memcpy(sig, tmp, sig_len); 133 return sig_len; 134 } 135