| /* LibTomCrypt, modular cryptographic library -- Tom St Denis |
| * |
| * LibTomCrypt is a library that provides various cryptographic |
| * algorithms in a highly modular and flexible manner. |
| * |
| * The library is free for all purposes without any express |
| * guarantee it works. |
| * |
| * Tom St Denis, tomstdenis@gmail.com, http://libtomcrypt.com |
| */ |
| #include "tomcrypt.h" |
| |
| /** |
| @file der_decode_integer.c |
| ASN.1 DER, decode an integer, Tom St Denis |
| */ |
| |
| |
| #ifdef LTC_DER |
| |
| /** |
| Read a mp_int integer |
| @param in The DER encoded data |
| @param inlen Size of DER encoded data |
| @param num The first mp_int to decode |
| @return CRYPT_OK if successful |
| */ |
| int der_decode_integer(const unsigned char *in, unsigned long inlen, void *num) |
| { |
| unsigned long x, y, z; |
| int err; |
| |
| LTC_ARGCHK(num != NULL); |
| LTC_ARGCHK(in != NULL); |
| |
| /* min DER INTEGER is 0x02 01 00 == 0 */ |
| if (inlen < (1 + 1 + 1)) { |
| return CRYPT_INVALID_PACKET; |
| } |
| |
| /* ok expect 0x02 when we AND with 0001 1111 [1F] */ |
| x = 0; |
| if ((in[x++] & 0x1F) != 0x02) { |
| return CRYPT_INVALID_PACKET; |
| } |
| |
| /* now decode the len stuff */ |
| z = in[x++]; |
| |
| if ((z & 0x80) == 0x00) { |
| /* short form */ |
| |
| /* will it overflow? */ |
| if (x + z > inlen) { |
| return CRYPT_INVALID_PACKET; |
| } |
| |
| /* no so read it */ |
| if ((err = mp_read_unsigned_bin(num, (unsigned char *)in + x, z)) != CRYPT_OK) { |
| return err; |
| } |
| } else { |
| /* long form */ |
| z &= 0x7F; |
| |
| /* will number of length bytes overflow? (or > 4) */ |
| if (((x + z) > inlen) || (z > 4) || (z == 0)) { |
| return CRYPT_INVALID_PACKET; |
| } |
| |
| /* now read it in */ |
| y = 0; |
| while (z--) { |
| y = ((unsigned long)(in[x++])) | (y << 8); |
| } |
| |
| /* now will reading y bytes overrun? */ |
| if ((x + y) > inlen) { |
| return CRYPT_INVALID_PACKET; |
| } |
| |
| /* no so read it */ |
| if ((err = mp_read_unsigned_bin(num, (unsigned char *)in + x, y)) != CRYPT_OK) { |
| return err; |
| } |
| } |
| |
| /* see if it's negative */ |
| if (in[x] & 0x80) { |
| void *tmp; |
| if (mp_init(&tmp) != CRYPT_OK) { |
| return CRYPT_MEM; |
| } |
| |
| if (mp_2expt(tmp, mp_count_bits(num)) != CRYPT_OK || mp_sub(num, tmp, num) != CRYPT_OK) { |
| mp_clear(tmp); |
| return CRYPT_MEM; |
| } |
| mp_clear(tmp); |
| } |
| |
| return CRYPT_OK; |
| |
| } |
| |
| #endif |
| |
| /* $Source: /cvs/libtom/libtomcrypt/src/pk/asn1/der/integer/der_decode_integer.c,v $ */ |
| /* $Revision: 1.4 $ */ |
| /* $Date: 2006/03/31 14:15:35 $ */ |