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 /* 28 * Compute ASN.1 encoded length for the provided integer. The ASN.1 29 * encoding is signed, so its leading bit must have value 0; it must 30 * also be of minimal length (so leading bytes of value 0 must be 31 * removed, except if that would contradict the rule about the sign 32 * bit). 33 */ 34 static size_t 35 asn1_int_length(const unsigned char *x, size_t xlen) 36 { 37 while (xlen > 0 && *x == 0) { 38 x ++; 39 xlen --; 40 } 41 if (xlen == 0 || *x >= 0x80) { 42 xlen ++; 43 } 44 return xlen; 45 } 46 47 /* see bearssl_ec.h */ 48 size_t 49 br_ecdsa_raw_to_asn1(void *sig, size_t sig_len) 50 { 51 /* 52 * Internal buffer is large enough to accommodate a signature 53 * such that r and s fit on 125 bytes each (signed encoding), 54 * meaning a curve order of up to 999 bits. This is the limit 55 * that ensures "simple" length encodings. 56 */ 57 unsigned char *buf; 58 size_t hlen, rlen, slen, zlen, off; 59 unsigned char tmp[257]; 60 61 buf = sig; 62 if ((sig_len & 1) != 0) { 63 return 0; 64 } 65 66 /* 67 * Compute lengths for the two integers. 68 */ 69 hlen = sig_len >> 1; 70 rlen = asn1_int_length(buf, hlen); 71 slen = asn1_int_length(buf + hlen, hlen); 72 if (rlen > 125 || slen > 125) { 73 return 0; 74 } 75 76 /* 77 * SEQUENCE header. 78 */ 79 tmp[0] = 0x30; 80 zlen = rlen + slen + 4; 81 if (zlen >= 0x80) { 82 tmp[1] = 0x81; 83 tmp[2] = zlen; 84 off = 3; 85 } else { 86 tmp[1] = zlen; 87 off = 2; 88 } 89 90 /* 91 * First INTEGER (r). 92 */ 93 tmp[off ++] = 0x02; 94 tmp[off ++] = rlen; 95 if (rlen > hlen) { 96 tmp[off] = 0x00; 97 memcpy(tmp + off + 1, buf, hlen); 98 } else { 99 memcpy(tmp + off, buf + hlen - rlen, rlen); 100 } 101 off += rlen; 102 103 /* 104 * Second INTEGER (s). 105 */ 106 tmp[off ++] = 0x02; 107 tmp[off ++] = slen; 108 if (slen > hlen) { 109 tmp[off] = 0x00; 110 memcpy(tmp + off + 1, buf + hlen, hlen); 111 } else { 112 memcpy(tmp + off, buf + sig_len - slen, slen); 113 } 114 off += slen; 115 116 /* 117 * Return ASN.1 signature. 118 */ 119 memcpy(sig, tmp, off); 120 return off; 121 } 122