Mercurial > dropbear
comparison libtomcrypt/src/pk/asn1/der/short_integer/der_encode_short_integer.c @ 285:1b9e69c058d2
propagate from branch 'au.asn.ucc.matt.ltc.dropbear' (head 20dccfc09627970a312d77fb41dc2970b62689c3)
to branch 'au.asn.ucc.matt.dropbear' (head fdf4a7a3b97ae5046139915de7e40399cceb2c01)
author | Matt Johnston <matt@ucc.asn.au> |
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date | Wed, 08 Mar 2006 13:23:58 +0000 |
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children | 0cbe8f6dbf9e |
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1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis | |
2 * | |
3 * LibTomCrypt is a library that provides various cryptographic | |
4 * algorithms in a highly modular and flexible manner. | |
5 * | |
6 * The library is free for all purposes without any express | |
7 * guarantee it works. | |
8 * | |
9 * Tom St Denis, [email protected], http://libtomcrypt.org | |
10 */ | |
11 #include "tomcrypt.h" | |
12 | |
13 /** | |
14 @file der_encode_short_integer.c | |
15 ASN.1 DER, encode an integer, Tom St Denis | |
16 */ | |
17 | |
18 | |
19 #ifdef LTC_DER | |
20 | |
21 /* Exports a positive integer as DER format (upto 32-bits in size) */ | |
22 /** | |
23 Store a mp_int integer | |
24 @param num The integer to encode | |
25 @param out [out] The destination for the DER encoded integers | |
26 @param outlen [in/out] The max size and resulting size of the DER encoded integers | |
27 @return CRYPT_OK if successful | |
28 */ | |
29 int der_encode_short_integer(unsigned long num, unsigned char *out, unsigned long *outlen) | |
30 { | |
31 unsigned long len, x, y, z; | |
32 int err; | |
33 | |
34 LTC_ARGCHK(out != NULL); | |
35 LTC_ARGCHK(outlen != NULL); | |
36 | |
37 /* force to 32 bits */ | |
38 num &= 0xFFFFFFFFUL; | |
39 | |
40 /* find out how big this will be */ | |
41 if ((err = der_length_short_integer(num, &len)) != CRYPT_OK) { | |
42 return err; | |
43 } | |
44 | |
45 if (*outlen < len) { | |
46 return CRYPT_BUFFER_OVERFLOW; | |
47 } | |
48 | |
49 /* get len of output */ | |
50 z = 0; | |
51 y = num; | |
52 while (y) { | |
53 ++z; | |
54 y >>= 8; | |
55 } | |
56 | |
57 /* handle zero */ | |
58 if (z == 0) { | |
59 z = 1; | |
60 } | |
61 | |
62 /* see if msb is set */ | |
63 z += (num&(1UL<<((z<<3) - 1))) ? 1 : 0; | |
64 | |
65 /* adjust the number so the msB is non-zero */ | |
66 for (x = 0; (z <= 4) && (x < (4 - z)); x++) { | |
67 num <<= 8; | |
68 } | |
69 | |
70 /* store header */ | |
71 x = 0; | |
72 out[x++] = 0x02; | |
73 out[x++] = z; | |
74 | |
75 /* if 31st bit is set output a leading zero and decrement count */ | |
76 if (z == 5) { | |
77 out[x++] = 0; | |
78 --z; | |
79 } | |
80 | |
81 /* store values */ | |
82 for (y = 0; y < z; y++) { | |
83 out[x++] = (num >> 24) & 0xFF; | |
84 num <<= 8; | |
85 } | |
86 | |
87 /* we good */ | |
88 *outlen = x; | |
89 | |
90 return CRYPT_OK; | |
91 } | |
92 | |
93 #endif | |
94 | |
95 /* $Source: /cvs/libtom/libtomcrypt/src/pk/asn1/der/short_integer/der_encode_short_integer.c,v $ */ | |
96 /* $Revision: 1.3 $ */ | |
97 /* $Date: 2005/05/23 01:27:03 $ */ |