sjcl-aws
Version:
Stanford Javascript Crypto Library
73 lines (68 loc) • 2.42 kB
JavaScript
/** @fileOverview CTR mode implementation
*
* @author Torben Haase
*/
if (sjcl.beware === undefined) {
sjcl.beware = {};
}
sjcl.beware["CTR mode is dangerous because it doesn't protect message integrity."
] = function() {
/**
* Dangerous: CTR mode.
* @namespace
* @author Torben Haase
*/
sjcl.mode.ctr = {
/** The name of the mode.
* @constant
*/
name: "ctr",
/** Encrypt in CTR mode.
* @param {Object} prf The pseudorandom function. It must have a block size of 16 bytes.
* @param {bitArray} plaintext The plaintext data.
* @param {bitArray} iv The initialization value. It must be 128 bits.
* @param {bitArray} [adata=[]] The authenticated data. Must be empty.
* @return The encrypted data, an array of bytes.
* @throws {sjcl.exception.invalid} if the IV isn't exactly 128 bits or if any adata is specified.
*/
encrypt: function(prf, plaintext, iv, adata) {
return sjcl.mode.ctr._calculate(prf, plaintext, iv, adata);
},
/** Decrypt in CTR mode.
* @param {Object} prf The pseudorandom function. It must have a block size of 16 bytes.
* @param {bitArray} ciphertext The ciphertext data.
* @param {bitArray} iv The initialization value. It must be 128 bits.
* @param {bitArray} [adata=[]] The authenticated data. It must be empty.
* @return The decrypted data, an array of bytes.
* @throws {sjcl.exception.invalid} if the IV isn't exactly 128 bits or if any adata is specified.
* @throws {sjcl.exception.corrupt} if if the message is corrupt.
*/
decrypt: function(prf, ciphertext, iv, adata) {
return sjcl.mode.ctr._calculate(prf, ciphertext, iv, adata);
},
_calculate: function(prf, data, iv, adata) {
var l, bl, res, c, d, e, i;
if (adata && adata.length) {
throw new sjcl.exception.invalid("ctr can't authenticate data");
}
if (sjcl.bitArray.bitLength(iv) !== 128) {
throw new sjcl.exception.invalid("ctr iv must be 128 bits");
}
if (!(l = data.length)) {
return [];
}
c = iv.slice(0);
d = data.slice(0);
bl = sjcl.bitArray.bitLength(d);
for (i=0; i<l; i+=4) {
e = prf.encrypt(c);
d[i] ^= e[0];
d[i+1] ^= e[1];
d[i+2] ^= e[2];
d[i+3] ^= e[3];
c[3]++;
}
return sjcl.bitArray.clamp(d, bl);
}
};
};