问题
So i read that in order to decrypt
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
i need to split it into 5 channels and solve for single-byte XOR keys,getting a candidate key of daeb1551e7. My question is how do you know how many different "channels" you need to split it into and where the splits occur.
回答1:
Solution to your encrypted message (see comment):
var cryptmsg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
var aCryptMsg=Array.from(cryptmsg);
var channelCount=8;
var channel=[];
var chanIndex=0;
function dec(nkey,ncrypt){
var ndec=nkey^ncrypt;
return ndec;
}
for(var i=0; i<channelCount; i++){
channel[i]=[];
}
while(aCryptMsg.length){
var buffer=aCryptMsg.splice(0,2).join("");
var ncrypt=parseInt(buffer,16);
channel[chanIndex].push(ncrypt);
chanIndex=(++chanIndex)%channelCount;
}
var goody=Object.create(null);
var alphanumerics=[[0x30,0x39],[0x41,0x5a],[0x61,0x7a]];
var alphabetical=[[0x41,0x5a],[0x61,0x7a]];
var currentRanges=alphanumerics;
currentRanges.forEach(function(range){
var indexStart=range[0];
var indexEnd=range[1];
for (var i=indexStart; i<=indexEnd; i++){
//table.push(String.fromCharCode(i));
var ch=String.fromCharCode(i);
goody[ch]=1;
}
});
(" ,.;:!\"'").split("").forEach(ch=>goody[ch]=1);
function findKeyCandidate(byteArray){
var keyResults=[];
for (var key=0; key<256; key++){
keyResults[key]=0;
byteArray.forEach(function(ncrypt){
var ndec=dec(key,ncrypt);
var dchar=String.fromCharCode(ndec);
if(goody[dchar]){
keyResults[key]++;
}
});
}
keyResults=keyResults.map(function(count,index){
return {key:index,count:count};
});
keyResults.sort(function(a,b){
return a.count-b.count;
});
return keyResults.pop().key;
}
var chanKey=channel.map(findKeyCandidate);
chanIndex=0;
var aDecrypMsg=[];
while(channel[chanIndex].length>0){
var ncrypt=channel[chanIndex].shift();
var nkey=chanKey[chanIndex];
var ndec=dec(nkey,ncrypt);
aDecrypMsg.push(ndec);
chanIndex=(++chanIndex)%channelCount;
}
aDecrypMsg.map(function(byte){return String.fromCharCode(byte)}).join("");
Decoded result:
/*
your flag is: 93ea36e84ba568b6590ec3b147d7a01e45b66202
On 17 March 1975, the proposed DES was published in the Federal Register. Public comments were requested, and in the following year two open workshops were held to discuss the proposed standard. There was some criticism from various parties, including from public-key cryptography pioneers Martin Hellman and Whitfield Diffie, citing a shortened key length and the mysterious "S-boxes" as evidence of improper interference from the NSA. The suspicion was that the algorithm had been covertly weakened by the intelligence agency so that they - but no-one else - could easily read encrypted messages. Alan Konheim (one of the designers of DES) commented, "We sent the S-boxes off to Washington. They came back and were all different." The United States Senate Select Committee on Intelligence reviewed the NSA's actions to determine whether there had been any improper involvement. In the unclassified summary of their findings, published in 1978, the Committee wrote:
In the development of DES, NSA convinced IBM that a reduced key size was sufficient; indirectly assisted in the development of the S-box structures; and certified that the final DES algorithm was, to the best of their knowledge, free from any statistical or mathematical weakness.
However, it also found that
NSA did not tamper with the design of the algorithm in any way. IBM invented and designed the algorithm, made all pertinent decisions regarding it, and concurred that the agreed upon key size was more than adequate for all commercial applications for which the DES was intended.
Another member of the DES team, Walter Tuchman, stated "We developed the DES algorithm entirely within IBM using IBMers. The NSA did not dictate a single wire!" In contrast, a declassified NSA book on cryptologic history states:
In 1973 NBS solicited private industry for a data encryption standard (DES). The first offerings were disappointing, so NSA began working on its own algorithm. Then Howard Rosenblum, deputy director for research and engineering, discovered that Walter Tuchman of IBM was working on a modification to Lucifer for general use. NSA gave Tuchman a clearance and brought him in to work jointly with the Agency on his Lucifer modification."
and
NSA worked closely with IBM to strengthen the algorithm against all except brute force attacks and to strengthen substitution tables, called S-boxes. Conversely, NSA tried to convince IBM to reduce the length of the key from 64 to 48 bits. Ultimately they compromised on a 56-bit key.
Some of the suspicions about hidden weaknesses in the S-boxes were allayed in 1990, with the independent discovery and open publication by Eli Biham and Adi Shamir of differential cryptanalysis, a general method for breaking block ciphers. The S-boxes of DES were much more resistant to the attack than if they had been chosen at random, strongly suggesting that IBM knew about the technique in the 1970s. This was indeed the case; in 1994, Don Coppersmith published some of the original design criteria for the S-boxes. According to Steven Levy, IBM Watson researchers discovered differential cryptanalytic attacks in 1974 and were asked by the NSA to keep the technique secret. Coppersmith explains IBM's secrecy decision by saying, "that was because [differential cryptanalysis] can be a very powerful tool, used against many schemes, and there was concern that such information in the public domain could adversely affect national security." Levy quotes Walter Tuchman: "[t]hey asked us to stamp all our documents confidential... We actually put a number on each one and locked them up in safes, because they were considered U.S. government classified. They said do it. So I did it". Bruce Schneier observed that "It took the academic community two decades to figure out that the NSA 'tweaks' actually improved the security of DES."
*/
回答2:
This is what I got, it's in javascript:
var cryptmsg="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";
var key="daeb1551e7";
var hexmsg=Array.from(cryptmsg);
var hexkey=Array.from(key);
var channels=[
];
while(hexkey.length){
var buffer=hexkey.splice(0,2);
var channel={
msg:[],
key:buffer.join("")
};
channels.push(channel);
}
var chanIndex=0;
while(hexmsg.length){
var buffer=hexmsg.splice(0,2);
channels[chanIndex].msg.push(buffer);
chanIndex++;
chanIndex=chanIndex%5;
}
var channelResults=channels.map(function(channel){
var nkey=parseInt(channel.key,16);
return channel.msg.map(
function(pair){return pair[0]+pair[1];}
).map(function(hexchar){
var nchar=parseInt(hexchar,16);
var ndec=nchar^nkey;
return String.fromCharCode(ndec);
});
});
var decodedMsg=[];
chanIndex=0
while(1){
var chresult=channelResults[chanIndex];
if(chresult.length<=0)break;
decodedMsg.push(chresult.shift());
chanIndex++;
chanIndex=chanIndex%5;
}
decodedMsg.join("");
Resulting decoded message:
/*
Bletchey Park rejoices in the fact that, until fairly recently, it was probably Britain's best kept secret. This is because of the secrecy surrounding all the activities carried on here during World War Two was of vital importance to our national security and ultimate victory.
*/
It turns out that each channel has it's own one byte key, and the 'message' for a particular channel is aggregated from bytes (hex pairs) taken round-robin from the original encrypted message (ie, byte 1 to channel 1, byte 2 to channel 2,..., byte 6 to channel 1). Decode with the one byte key. Then reconstruct the final decrypted message by reversing the process taken when we 'collated' the encrypted message bytes into their channels.
update
compact version:
var cryptmsg="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";
var key="daeb1551e7";
var aCryptMsg=Array.prototype.slice.call(cryptmsg);
var aKey=Array.prototype.slice.call(key);
var chanKey=[];
var chanIndex=0;
var aDecryptMsg=[];
function dec(nkey,ncrypt){
var ndec=nkey^ncrypt;
return String.fromCharCode(ndec);
}
while(aKey.length){
var buffer=aKey.splice(0,2);
var nkey=parseInt(buffer.join(""),16);
chanKey.push(nkey);
}
while(aCryptMsg.length){
var buffer=aCryptMsg.splice(0,2);
var ncrypt=parseInt(buffer.join(""),16);
var debuf=dec(chanKey[chanIndex],ncrypt);
aDecryptMsg.push(debuf);
chanIndex=(++chanIndex)%5;
}
aDecryptMsg.join("");
/*
Bletchey Park rejoices in the fact that, until fairly recently, it was probably Britain's best kept secret. This is because of the secrecy surrounding all the activities carried on here during World War Two was of vital importance to our national security and ultimate victory.
*/
回答3:
Here's how to determine how many channels:
Take your encrypted sequence of bytes and shift it one place to the right. Pad with a 0x00 on the left. Then XOR the result with the original string and count the number of zero bits. If the zero bits are about 65% of the bits, then the key has one byte. If the zero bits are about 50% of the bits, then the key does not have one byte, and we try again.
Take the original encrypted sequence of bytes and shift it two places to the right. Pad with 0x0000 on the left. XOR the result with the original. If you get 65% zero bits, the key has two bytes. If 50%, then not two bytes.
Continue until you find the number of byres in the key.
For your message, these were the percentages:
1-byte shift: 48.4% 2-byte shift: 47.1% 3-byte shift: 47.5% 4-byte shift: 48.6% 5-byte shift: 66.7% <-- 6-byte shift: 47.7%
So the key is likely to have a length of 5 bytes.
The reason this works is that there are more coincidences when shifted by the same length as the key. More coincidences when XORed means more zeroes.
来源：https://stackoverflow.com/questions/26600192/decoding-hexadecimal-xor-encryption