1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
|
/*
Grab an RSA public key from the file given as an argument, grab a message
from another file, and encrypt the message.
Algorithms used:
RSA with EME1(SHA-1) padding to encrypt the master key
CAST-128 in CBC mode with PKCS#7 padding to encrypt the message.
HMAC with SHA-1 is used to authenticate the message
The keys+IV used are derived from the master key (the thing that's encrypted
with RSA) using KDF2(SHA-1). The 3 outputs of KDF2 are parameterized by P,
where P is "CAST", "IV" or "MAC", in order to make each key/IV unique.
The format is:
1) First line is the master key, encrypted with the recipients public key
using EME1(SHA-1), and then base64 encoded.
2) Second line is the first 96 bits (12 bytes) of the HMAC(SHA-1) of
the _plaintext_
3) Following lines are base64 encoded ciphertext (CAST-128 as described),
each broken after ~72 characters.
Written by Jack Lloyd (lloyd@randombit.net), June 3, 2002
Updated to use KDF2, September 8, 2002
Updated to read X.509 keys, October 21, 2002
This file is in the public domain
*/
#include <iostream>
#include <fstream>
#include <string>
#include <memory>
#include <botan/botan.h>
#include <botan/look_pk.h>
#include <botan/rsa.h>
using namespace Botan;
std::string b64_encode(const SecureVector<byte>&);
SymmetricKey derive_key(const std::string&, const SymmetricKey&, u32bit);
int main(int argc, char* argv[])
{
if(argc != 3)
{
std::cout << "Usage: " << argv[0] << " keyfile messagefile" << std::endl;
return 1;
}
std::ifstream message(argv[2]);
if(!message)
{
std::cout << "Couldn't read the message file." << std::endl;
return 1;
}
std::string output_name(argv[2]);
output_name += ".enc";
std::ofstream ciphertext(output_name.c_str());
if(!ciphertext)
{
std::cout << "Couldn't write the ciphertext to " << output_name
<< std::endl;
return 1;
}
try {
std::auto_ptr<X509_PublicKey> key(X509::load_key(argv[1]));
RSA_PublicKey* rsakey = dynamic_cast<RSA_PublicKey*>(key.get());
if(!rsakey)
{
std::cout << "The loaded key is not a RSA key!\n";
return 1;
}
std::auto_ptr<RandomNumberGenerator> rng(
RandomNumberGenerator::make_rng());
std::auto_ptr<PK_Encryptor> encryptor(get_pk_encryptor(*rsakey,
"EME1(SHA-1)"));
/* Generate the master key (the other keys are derived from this)
Basically, make the key as large as can be encrypted by this key, up
to a limit of 256 bits. For 512 bit keys, the master key will be >160
bits. A >600 bit key will use the full 256 bit master key.
In theory, this is not enough, because we derive 16+16+8=40 bytes of
secrets (if you include the IV) using the master key, so they are not
statistically indepedent. Practically speaking I don't think this is
a problem.
*/
SymmetricKey masterkey(*rng,
std::min(32U, encryptor->maximum_input_size()));
SymmetricKey cast_key = derive_key("CAST", masterkey, 16);
SymmetricKey mac_key = derive_key("MAC", masterkey, 16);
SymmetricKey iv = derive_key("IV", masterkey, 8);
SecureVector<byte> encrypted_key =
encryptor->encrypt(masterkey.bits_of(), *rng);
ciphertext << b64_encode(encrypted_key) << std::endl;
Pipe pipe(new Fork(
new Chain(
get_cipher("CAST-128/CBC/PKCS7", cast_key, iv,
ENCRYPTION),
new Base64_Encoder(true) // true == do linebreaking
),
new Chain(
new MAC_Filter("HMAC(SHA-1)", mac_key, 12),
new Base64_Encoder
)
)
);
pipe.start_msg();
message >> pipe;
pipe.end_msg();
/* Write the MAC as the second line. That way we can pull it off right
from the start, and feed the rest of the file right into a pipe on the
decrypting end.
*/
ciphertext << pipe.read_all_as_string(1) << std::endl;
ciphertext << pipe.read_all_as_string(0);
}
catch(std::exception& e)
{
std::cout << "Exception: " << e.what() << std::endl;
}
return 0;
}
std::string b64_encode(const SecureVector<byte>& in)
{
Pipe pipe(new Base64_Encoder);
pipe.process_msg(in);
return pipe.read_all_as_string();
}
SymmetricKey derive_key(const std::string& param,
const SymmetricKey& masterkey,
u32bit outputlength)
{
std::auto_ptr<KDF> kdf(get_kdf("KDF2(SHA-1)"));
return kdf->derive_key(outputlength, masterkey.bits_of(), param);
}
|
