Botan 2.19.1
Crypto and TLS for C&
eme_pkcs.cpp
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1/*
2* PKCS #1 v1.5 Type 2 (encryption) padding
3* (C) 1999-2007,2015,2016 Jack Lloyd
4*
5* Botan is released under the Simplified BSD License (see license.txt)
6*/
7
8#include <botan/eme_pkcs.h>
9#include <botan/exceptn.h>
10#include <botan/rng.h>
11#include <botan/internal/ct_utils.h>
12
13namespace Botan {
14
15/*
16* PKCS1 Pad Operation
17*/
18secure_vector<uint8_t> EME_PKCS1v15::pad(const uint8_t in[], size_t inlen,
19 size_t key_length,
20 RandomNumberGenerator& rng) const
21 {
22 key_length /= 8;
23
24 if(inlen > maximum_input_size(key_length * 8))
25 {
26 throw Invalid_Argument("PKCS1: Input is too large");
27 }
28
29 secure_vector<uint8_t> out(key_length);
30
31 out[0] = 0x02;
32 rng.randomize(out.data() + 1, (key_length - inlen - 2));
33
34 for(size_t j = 1; j != key_length - inlen - 1; ++j)
35 {
36 if(out[j] == 0)
37 {
38 out[j] = rng.next_nonzero_byte();
39 }
40 }
41
42 buffer_insert(out, key_length - inlen, in, inlen);
43
44 return out;
45 }
46
47/*
48* PKCS1 Unpad Operation
49*/
51 const uint8_t in[], size_t inlen) const
52 {
53 /*
54 * RSA decryption pads the ciphertext up to the modulus size, so this only
55 * occurs with very (!) small keys, or when fuzzing.
56 *
57 * 11 bytes == 00,02 + 8 bytes mandatory padding + 00
58 */
59 if(inlen < 11)
60 {
61 valid_mask = false;
63 }
64
65 CT::poison(in, inlen);
66
69 size_t delim_idx = 2; // initial 0002
70
71 bad_input_m |= ~CT::Mask<uint8_t>::is_equal(in[0], 0);
72 bad_input_m |= ~CT::Mask<uint8_t>::is_equal(in[1], 2);
73
74 for(size_t i = 2; i < inlen; ++i)
75 {
76 const auto is_zero_m = CT::Mask<uint8_t>::is_zero(in[i]);
77 delim_idx += seen_zero_m.if_not_set_return(1);
78 seen_zero_m |= is_zero_m;
79 }
80
81 // no zero delim -> bad padding
82 bad_input_m |= ~seen_zero_m;
83 /*
84 delim indicates < 8 bytes padding -> bad padding
85
86 We require 11 here because we are counting also the 00 delim byte
87 */
88 bad_input_m |= CT::Mask<uint8_t>(CT::Mask<size_t>::is_lt(delim_idx, 11));
89
90 valid_mask = (~bad_input_m).unpoisoned_value();
91 const secure_vector<uint8_t> output = CT::copy_output(bad_input_m, in, inlen, delim_idx);
92
93 CT::unpoison(in, inlen);
94
95 return output;
96 }
97
98/*
99* Return the max input size for a given key size
100*/
101size_t EME_PKCS1v15::maximum_input_size(size_t keybits) const
102 {
103 if(keybits / 8 > 10)
104 return ((keybits / 8) - 10);
105 else
106 return 0;
107 }
108
109}
static Mask< T > is_zero(T x)
Definition: ct_utils.h:141
T if_not_set_return(T x) const
Definition: ct_utils.h:280
static Mask< T > cleared()
Definition: ct_utils.h:115
secure_vector< uint8_t > pad(const uint8_t[], size_t, size_t, RandomNumberGenerator &) const override
Definition: eme_pkcs.cpp:18
size_t maximum_input_size(size_t) const override
Definition: eme_pkcs.cpp:101
secure_vector< uint8_t > unpad(uint8_t &valid_mask, const uint8_t in[], size_t in_len) const override
Definition: eme_pkcs.cpp:50
uint8_t next_nonzero_byte()
Definition: rng.h:171
virtual void randomize(uint8_t output[], size_t length)=0
void poison(const T *p, size_t n)
Definition: ct_utils.h:48
secure_vector< uint8_t > copy_output(CT::Mask< uint8_t > bad_input, const uint8_t input[], size_t input_length, size_t offset)
Definition: ct_utils.cpp:13
void unpoison(const T *p, size_t n)
Definition: ct_utils.h:59
Definition: alg_id.cpp:13
size_t buffer_insert(std::vector< T, Alloc > &buf, size_t buf_offset, const T input[], size_t input_length)
Definition: mem_ops.h:228
std::vector< T, secure_allocator< T > > secure_vector
Definition: secmem.h:65