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
|
package org.spongycastle.crypto.engines;
import java.math.BigInteger;
import java.security.SecureRandom;
import org.spongycastle.crypto.AsymmetricBlockCipher;
import org.spongycastle.crypto.CipherParameters;
import org.spongycastle.crypto.DataLengthException;
import org.spongycastle.crypto.params.ParametersWithRandom;
import org.spongycastle.crypto.params.RSAKeyParameters;
import org.spongycastle.crypto.params.RSAPrivateCrtKeyParameters;
import org.spongycastle.util.BigIntegers;
/**
* this does your basic RSA algorithm with blinding
*/
public class RSABlindedEngine
implements AsymmetricBlockCipher
{
private static final BigInteger ONE = BigInteger.valueOf(1);
private RSACoreEngine core = new RSACoreEngine();
private RSAKeyParameters key;
private SecureRandom random;
/**
* initialise the RSA engine.
*
* @param forEncryption true if we are encrypting, false otherwise.
* @param param the necessary RSA key parameters.
*/
public void init(
boolean forEncryption,
CipherParameters param)
{
core.init(forEncryption, param);
if (param instanceof ParametersWithRandom)
{
ParametersWithRandom rParam = (ParametersWithRandom)param;
key = (RSAKeyParameters)rParam.getParameters();
random = rParam.getRandom();
}
else
{
key = (RSAKeyParameters)param;
random = new SecureRandom();
}
}
/**
* Return the maximum size for an input block to this engine.
* For RSA this is always one byte less than the key size on
* encryption, and the same length as the key size on decryption.
*
* @return maximum size for an input block.
*/
public int getInputBlockSize()
{
return core.getInputBlockSize();
}
/**
* Return the maximum size for an output block to this engine.
* For RSA this is always one byte less than the key size on
* decryption, and the same length as the key size on encryption.
*
* @return maximum size for an output block.
*/
public int getOutputBlockSize()
{
return core.getOutputBlockSize();
}
/**
* Process a single block using the basic RSA algorithm.
*
* @param in the input array.
* @param inOff the offset into the input buffer where the data starts.
* @param inLen the length of the data to be processed.
* @return the result of the RSA process.
* @exception DataLengthException the input block is too large.
*/
public byte[] processBlock(
byte[] in,
int inOff,
int inLen)
{
if (key == null)
{
throw new IllegalStateException("RSA engine not initialised");
}
BigInteger input = core.convertInput(in, inOff, inLen);
BigInteger result;
if (key instanceof RSAPrivateCrtKeyParameters)
{
RSAPrivateCrtKeyParameters k = (RSAPrivateCrtKeyParameters)key;
BigInteger e = k.getPublicExponent();
if (e != null) // can't do blinding without a public exponent
{
BigInteger m = k.getModulus();
BigInteger r = BigIntegers.createRandomInRange(ONE, m.subtract(ONE), random);
BigInteger blindedInput = r.modPow(e, m).multiply(input).mod(m);
BigInteger blindedResult = core.processBlock(blindedInput);
BigInteger rInv = r.modInverse(m);
result = blindedResult.multiply(rInv).mod(m);
}
else
{
result = core.processBlock(input);
}
}
else
{
result = core.processBlock(input);
}
return core.convertOutput(result);
}
}
|
