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minor optimizations in cfb mode

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This commit is contained in:
Tankred Hase 2014-02-24 21:12:59 +01:00
parent af5f1e89f0
commit d0c319dd49
1 changed files with 12 additions and 5 deletions
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17
src/crypto/cfb.js
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@ -52,7 +52,7 @@ module.exports = {
prefixrandom = prefixrandom + prefixrandom.charAt(block_size - 2) + prefixrandom.charAt(block_size - 1); prefixrandom = prefixrandom + prefixrandom.charAt(block_size - 2) + prefixrandom.charAt(block_size - 1);
util.print_debug("prefixrandom:" + util.hexstrdump(prefixrandom)); util.print_debug("prefixrandom:" + util.hexstrdump(prefixrandom));
var ciphertext = ""; var ciphertext = "";
var i; var i, n;
// 1. The feedback register (FR) is set to the IV, which is all zeros. // 1. The feedback register (FR) is set to the IV, which is all zeros.
for (i = 0; i < block_size; i++) FR[i] = 0; for (i = 0; i < block_size; i++) FR[i] = 0;
@ -110,12 +110,18 @@ module.exports = {
// 9. FRE is xored with the first 8 octets of the given plaintext, now // 9. FRE is xored with the first 8 octets of the given plaintext, now
// that we have finished encrypting the 10 octets of prefixed data. // that we have finished encrypting the 10 octets of prefixed data.
// This produces C11-C18, the next 8 octets of ciphertext. // This produces C11-C18, the next 8 octets of ciphertext.
for (i = 2; i < block_size; i++) ciphertext += String.fromCharCode(FRE[i] ^ plaintext.charCodeAt(i)); for (i = 2; i < block_size; i++) {
ciphertext += String.fromCharCode(FRE[i] ^ plaintext.charCodeAt(i));
}
var tempCiphertext = ciphertext.substring(0, 2 * block_size).split(''); var tempCiphertext = ciphertext.substring(0, 2 * block_size).split('');
var tempCiphertextString = ciphertext.substring(block_size); var tempCiphertextString = ciphertext.substring(block_size);
var tempCiphertextBlock;
for (n = block_size; n < plaintext.length; n += block_size) { for (n = block_size; n < plaintext.length; n += block_size) {
// 10. FR is loaded with C11-C18 // 10. FR is loaded with C11-C18
for (i = 0; i < block_size; i++) FR[i] = tempCiphertextString.charCodeAt(i); for (i = 0; i < block_size; i++) {
FR[i] = tempCiphertextString.charCodeAt(i);
}
tempCiphertextString = ''; tempCiphertextString = '';
// 11. FR is encrypted to produce FRE. // 11. FR is encrypted to produce FRE.
@ -125,8 +131,9 @@ module.exports = {
// next 8 octets of ciphertext. These are loaded into FR and the // next 8 octets of ciphertext. These are loaded into FR and the
// process is repeated until the plaintext is used up. // process is repeated until the plaintext is used up.
for (i = 0; i < block_size; i++) { for (i = 0; i < block_size; i++) {
tempCiphertext.push(String.fromCharCode(FRE[i] ^ plaintext.charCodeAt(n + i))); tempCiphertextBlock = String.fromCharCode(FRE[i] ^ plaintext.charCodeAt(n + i));
tempCiphertextString += String.fromCharCode(FRE[i] ^ plaintext.charCodeAt(n + i)); tempCiphertext[tempCiphertext.length] = tempCiphertextBlock;
tempCiphertextString += tempCiphertextBlock;
} }
} }
ciphertext = tempCiphertext.join(''); ciphertext = tempCiphertext.join('');