Mercurial > dropbear
diff der_decode_integer.c @ 143:5d99163f7e32 libtomcrypt-orig
import of libtomcrypt 0.99
author | Matt Johnston <matt@ucc.asn.au> |
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date | Sun, 19 Dec 2004 11:34:45 +0000 |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/der_decode_integer.c Sun Dec 19 11:34:45 2004 +0000 @@ -0,0 +1,83 @@ +/* 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, [email protected], http://libtomcrypt.org + */ + +#include "mycrypt.h" + + +/* decodes a DER INTEGER in [in]. You have to tell this function + * how many bytes are available [inlen]. It will then attempt to + * read the INTEGER. If all goes well it stores the number of bytes + * read in [inlen] and the number in [num]. + */ +int der_decode_integer(const unsigned char *in, unsigned long *inlen, mp_int *num) +{ + unsigned long tmplen, y, z; + + _ARGCHK(num != NULL); + _ARGCHK(in != NULL); + _ARGCHK(inlen != NULL); + + /* save copy of max output size */ + tmplen = *inlen; + *inlen = 0; + + /* min DER INTEGER is 0x02 01 00 == 0 */ + if (tmplen < (1 + 1 + 1)) { + return CRYPT_INVALID_PACKET; + } + + /* ok expect 0x02 when we AND with 0011 1111 [3F] */ + if ((*in++ & 0x3F) != 0x02) { + return CRYPT_INVALID_PACKET; + } + ++(*inlen); + + /* now decode the len stuff */ + z = *in++; + ++(*inlen); + + if ((z & 0x80) == 0x00) { + /* short form */ + + /* will it overflow? */ + if (*inlen + z > tmplen) { + return CRYPT_INVALID_PACKET; + } + + /* no so read it */ + (*inlen) += z; + return mpi_to_ltc_error(mp_read_unsigned_bin(num, (unsigned char *)in, z)); + } else { + /* long form */ + z &= 0x7F; + + /* will number of length bytes overflow? (or > 4) */ + if (((*inlen + z) > tmplen) || (z > 4)) { + return CRYPT_INVALID_PACKET; + } + + /* now read it in */ + y = 0; + while (z--) { + y = ((unsigned long)(*in++)) | (y << 8); + ++(*inlen); + } + + /* now will reading y bytes overrun? */ + if ((*inlen + y) > tmplen) { + return CRYPT_INVALID_PACKET; + } + + /* no so read it */ + (*inlen) += y; + return mpi_to_ltc_error(mp_read_unsigned_bin(num, (unsigned char *)in, y)); + } +}