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Better crypto key length recovery.

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This commit is contained in:
Yury Delendik 2015-12-29 15:10:38 -06:00
parent 17780dab31
commit c991480687
3 changed files with 31 additions and 1 deletions
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23
src/core/crypto.js
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@ -38,6 +38,7 @@ var utf8StringToString = sharedUtil.utf8StringToString;
var warn = sharedUtil.warn;
var Name = corePrimitives.Name;
var isName = corePrimitives.isName;
var isDict = corePrimitives.isDict;
var DecryptStream = coreStream.DecryptStream;
var ARCFourCipher = (function ARCFourCipherClosure() {
@ -1921,7 +1922,27 @@ var CipherTransformFactory = (function CipherTransformFactoryClosure() {
error('unsupported encryption algorithm');
}
this.algorithm = algorithm;
var keyLength = dict.get('Length') || 40;
var keyLength = dict.get('Length');
if (!keyLength) {
// Spec asks to rely on encryption dictionary's Length entry, however
// some PDFs don't have it. Trying to recover.
if (algorithm <= 3) {
// For 1 and 2 it's fixed to 40-bit, for 3 40-bit is a minimal value.
keyLength = 40;
} else {
// Trying to find default handler -- it usually has Length.
var cfDict = dict.get('CF');
var streamCryptoName = dict.get('StmF');
if (isDict(cfDict) && isName(streamCryptoName)) {
var handlerDict = cfDict.get(streamCryptoName.name);
keyLength = (handlerDict && handlerDict.get('Length')) || 128;
if (keyLength < 40) {
// Sometimes it's incorrect value of bits, generators specify bytes.
keyLength <<= 3;
}
}
}
}
if (!isInt(keyLength) ||
keyLength < 40 || (keyLength % 8) !== 0) {
error('invalid key length');