Source Code Cross Referenced for RC6Engine.java in  » Security » Bouncy-Castle » org » bouncycastle » crypto » engines » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » Security » Bouncy Castle » org.bouncycastle.crypto.engines 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        package org.bouncycastle.crypto.engines;
002:
003:        import org.bouncycastle.crypto.BlockCipher;
004:        import org.bouncycastle.crypto.CipherParameters;
005:        import org.bouncycastle.crypto.DataLengthException;
006:        import org.bouncycastle.crypto.params.KeyParameter;
007:
008:        /**
009:         * An RC6 engine.
010:         */
011:        public class RC6Engine implements  BlockCipher {
012:            private static final int wordSize = 32;
013:            private static final int bytesPerWord = wordSize / 8;
014:
015:            /*
016:             * the number of rounds to perform
017:             */
018:            private static final int _noRounds = 20;
019:
020:            /*
021:             * the expanded key array of size 2*(rounds + 1)
022:             */
023:            private int _S[];
024:
025:            /*
026:             * our "magic constants" for wordSize 32
027:             *
028:             * Pw = Odd((e-2) * 2^wordsize)
029:             * Qw = Odd((o-2) * 2^wordsize)
030:             *
031:             * where e is the base of natural logarithms (2.718281828...)
032:             * and o is the golden ratio (1.61803398...)
033:             */
034:            private static final int P32 = 0xb7e15163;
035:            private static final int Q32 = 0x9e3779b9;
036:
037:            private static final int LGW = 5; // log2(32)
038:
039:            private boolean forEncryption;
040:
041:            /**
042:             * Create an instance of the RC6 encryption algorithm
043:             * and set some defaults
044:             */
045:            public RC6Engine() {
046:                _S = null;
047:            }
048:
049:            public String getAlgorithmName() {
050:                return "RC6";
051:            }
052:
053:            public int getBlockSize() {
054:                return 4 * bytesPerWord;
055:            }
056:
057:            /**
058:             * initialise a RC5-32 cipher.
059:             *
060:             * @param forEncryption whether or not we are for encryption.
061:             * @param params the parameters required to set up the cipher.
062:             * @exception IllegalArgumentException if the params argument is
063:             * inappropriate.
064:             */
065:            public void init(boolean forEncryption, CipherParameters params) {
066:                if (!(params instanceof  KeyParameter)) {
067:                    throw new IllegalArgumentException(
068:                            "invalid parameter passed to RC6 init - "
069:                                    + params.getClass().getName());
070:                }
071:
072:                KeyParameter p = (KeyParameter) params;
073:                this .forEncryption = forEncryption;
074:                setKey(p.getKey());
075:            }
076:
077:            public int processBlock(byte[] in, int inOff, byte[] out, int outOff) {
078:                int blockSize = getBlockSize();
079:                if (_S == null) {
080:                    throw new IllegalStateException(
081:                            "RC6 engine not initialised");
082:                }
083:                if ((inOff + blockSize) > in.length) {
084:                    throw new DataLengthException("input buffer too short");
085:                }
086:                if ((outOff + blockSize) > out.length) {
087:                    throw new DataLengthException("output buffer too short");
088:                }
089:
090:                return (forEncryption) ? encryptBlock(in, inOff, out, outOff)
091:                        : decryptBlock(in, inOff, out, outOff);
092:            }
093:
094:            public void reset() {
095:            }
096:
097:            /**
098:             * Re-key the cipher.
099:             * <p>
100:             * @param  inKey  the key to be used
101:             */
102:            private void setKey(byte[] key) {
103:
104:                //
105:                // KEY EXPANSION:
106:                //
107:                // There are 3 phases to the key expansion.
108:                //
109:                // Phase 1:
110:                //   Copy the secret key K[0...b-1] into an array L[0..c-1] of
111:                //   c = ceil(b/u), where u = wordSize/8 in little-endian order.
112:                //   In other words, we fill up L using u consecutive key bytes
113:                //   of K. Any unfilled byte positions in L are zeroed. In the
114:                //   case that b = c = 0, set c = 1 and L[0] = 0.
115:                //
116:                // compute number of dwords
117:                int c = (key.length + (bytesPerWord - 1)) / bytesPerWord;
118:                if (c == 0) {
119:                    c = 1;
120:                }
121:                int[] L = new int[(key.length + bytesPerWord - 1)
122:                        / bytesPerWord];
123:
124:                // load all key bytes into array of key dwords
125:                for (int i = key.length - 1; i >= 0; i--) {
126:                    L[i / bytesPerWord] = (L[i / bytesPerWord] << 8)
127:                            + (key[i] & 0xff);
128:                }
129:
130:                //
131:                // Phase 2:
132:                //   Key schedule is placed in a array of 2+2*ROUNDS+2 = 44 dwords.
133:                //   Initialize S to a particular fixed pseudo-random bit pattern
134:                //   using an arithmetic progression modulo 2^wordsize determined
135:                //   by the magic numbers, Pw & Qw.
136:                //
137:                _S = new int[2 + 2 * _noRounds + 2];
138:
139:                _S[0] = P32;
140:                for (int i = 1; i < _S.length; i++) {
141:                    _S[i] = (_S[i - 1] + Q32);
142:                }
143:
144:                //
145:                // Phase 3:
146:                //   Mix in the user's secret key in 3 passes over the arrays S & L.
147:                //   The max of the arrays sizes is used as the loop control
148:                //
149:                int iter;
150:
151:                if (L.length > _S.length) {
152:                    iter = 3 * L.length;
153:                } else {
154:                    iter = 3 * _S.length;
155:                }
156:
157:                int A = 0;
158:                int B = 0;
159:                int i = 0, j = 0;
160:
161:                for (int k = 0; k < iter; k++) {
162:                    A = _S[i] = rotateLeft(_S[i] + A + B, 3);
163:                    B = L[j] = rotateLeft(L[j] + A + B, A + B);
164:                    i = (i + 1) % _S.length;
165:                    j = (j + 1) % L.length;
166:                }
167:            }
168:
169:            private int encryptBlock(byte[] in, int inOff, byte[] out,
170:                    int outOff) {
171:                // load A,B,C and D registers from in.
172:                int A = bytesToWord(in, inOff);
173:                int B = bytesToWord(in, inOff + bytesPerWord);
174:                int C = bytesToWord(in, inOff + bytesPerWord * 2);
175:                int D = bytesToWord(in, inOff + bytesPerWord * 3);
176:
177:                // Do pseudo-round #0: pre-whitening of B and D
178:                B += _S[0];
179:                D += _S[1];
180:
181:                // perform round #1,#2 ... #ROUNDS of encryption 
182:                for (int i = 1; i <= _noRounds; i++) {
183:                    int t = 0, u = 0;
184:
185:                    t = B * (2 * B + 1);
186:                    t = rotateLeft(t, 5);
187:
188:                    u = D * (2 * D + 1);
189:                    u = rotateLeft(u, 5);
190:
191:                    A ^= t;
192:                    A = rotateLeft(A, u);
193:                    A += _S[2 * i];
194:
195:                    C ^= u;
196:                    C = rotateLeft(C, t);
197:                    C += _S[2 * i + 1];
198:
199:                    int temp = A;
200:                    A = B;
201:                    B = C;
202:                    C = D;
203:                    D = temp;
204:                }
205:                // do pseudo-round #(ROUNDS+1) : post-whitening of A and C
206:                A += _S[2 * _noRounds + 2];
207:                C += _S[2 * _noRounds + 3];
208:
209:                // store A, B, C and D registers to out        
210:                wordToBytes(A, out, outOff);
211:                wordToBytes(B, out, outOff + bytesPerWord);
212:                wordToBytes(C, out, outOff + bytesPerWord * 2);
213:                wordToBytes(D, out, outOff + bytesPerWord * 3);
214:
215:                return 4 * bytesPerWord;
216:            }
217:
218:            private int decryptBlock(byte[] in, int inOff, byte[] out,
219:                    int outOff) {
220:                // load A,B,C and D registers from out.
221:                int A = bytesToWord(in, inOff);
222:                int B = bytesToWord(in, inOff + bytesPerWord);
223:                int C = bytesToWord(in, inOff + bytesPerWord * 2);
224:                int D = bytesToWord(in, inOff + bytesPerWord * 3);
225:
226:                // Undo pseudo-round #(ROUNDS+1) : post whitening of A and C 
227:                C -= _S[2 * _noRounds + 3];
228:                A -= _S[2 * _noRounds + 2];
229:
230:                // Undo round #ROUNDS, .., #2,#1 of encryption 
231:                for (int i = _noRounds; i >= 1; i--) {
232:                    int t = 0, u = 0;
233:
234:                    int temp = D;
235:                    D = C;
236:                    C = B;
237:                    B = A;
238:                    A = temp;
239:
240:                    t = B * (2 * B + 1);
241:                    t = rotateLeft(t, LGW);
242:
243:                    u = D * (2 * D + 1);
244:                    u = rotateLeft(u, LGW);
245:
246:                    C -= _S[2 * i + 1];
247:                    C = rotateRight(C, t);
248:                    C ^= u;
249:
250:                    A -= _S[2 * i];
251:                    A = rotateRight(A, u);
252:                    A ^= t;
253:
254:                }
255:                // Undo pseudo-round #0: pre-whitening of B and D
256:                D -= _S[1];
257:                B -= _S[0];
258:
259:                wordToBytes(A, out, outOff);
260:                wordToBytes(B, out, outOff + bytesPerWord);
261:                wordToBytes(C, out, outOff + bytesPerWord * 2);
262:                wordToBytes(D, out, outOff + bytesPerWord * 3);
263:
264:                return 4 * bytesPerWord;
265:            }
266:
267:            //////////////////////////////////////////////////////////////
268:            //
269:            // PRIVATE Helper Methods
270:            //
271:            //////////////////////////////////////////////////////////////
272:
273:            /**
274:             * Perform a left "spin" of the word. The rotation of the given
275:             * word <em>x</em> is rotated left by <em>y</em> bits.
276:             * Only the <em>lg(wordSize)</em> low-order bits of <em>y</em>
277:             * are used to determine the rotation amount. Here it is 
278:             * assumed that the wordsize used is 32.
279:             * <p>
280:             * @param  x  word to rotate
281:             * @param  y    number of bits to rotate % wordSize
282:             */
283:            private int rotateLeft(int x, int y) {
284:                return (x << y) | (x >>> -y);
285:            }
286:
287:            /**
288:             * Perform a right "spin" of the word. The rotation of the given
289:             * word <em>x</em> is rotated left by <em>y</em> bits.
290:             * Only the <em>lg(wordSize)</em> low-order bits of <em>y</em>
291:             * are used to determine the rotation amount. Here it is 
292:             * assumed that the wordsize used is a power of 2.
293:             * <p>
294:             * @param  x  word to rotate
295:             * @param  y    number of bits to rotate % wordSize
296:             */
297:            private int rotateRight(int x, int y) {
298:                return (x >>> y) | (x << -y);
299:            }
300:
301:            private int bytesToWord(byte[] src, int srcOff) {
302:                int word = 0;
303:
304:                for (int i = bytesPerWord - 1; i >= 0; i--) {
305:                    word = (word << 8) + (src[i + srcOff] & 0xff);
306:                }
307:
308:                return word;
309:            }
310:
311:            private void wordToBytes(int word, byte[] dst, int dstOff) {
312:                for (int i = 0; i < bytesPerWord; i++) {
313:                    dst[i + dstOff] = (byte) word;
314:                    word >>>= 8;
315:                }
316:            }
317:        }
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