How to determine what type of encoding/encryption has been used?

Question

Is there a way to find what type of encryption/encoding is being used? For example, I am testing a web application which stores the password in the database in an encrypted format (WeJcFMQ/8+8QJ/w0hHh+0g==). How do I determine what hashing or encryption is being used?

Answer 1

Your example string (WeJcFMQ/8+8QJ/w0hHh+0g==) is Base64 encoding for a sequence of 16 bytes, which do not look like meaningful ASCII or UTF-8. If this is a value stored for password verification (i.e. not really an "encrypted" password, rather a "hashed" password) then this is probably the result of a hash function computed over the password; the one classical hash function with a 128-bit output is MD5. But it could be about anything.

The "normal" way to know that is to look at the application code. Application code is incarnated in a tangible, fat way (executable files on a server, source code somewhere...) which is not, and cannot be, as much protected as a secret key can. So reverse engineering is the "way to go".

Barring reverse engineering, you can make a few experiments to try to make educated guesses:

• If the same user "changes" his password but reuses the same, does the stored value changes ? If yes, then part of the value is probably a randomized "salt" or IV (assuming symmetric encryption).
• Assuming that the value is deterministic from the password for a given user, if two users choose the same password, does it result in the same stored value ? If no, then the user name is probably part of the computation. You may want to try to compute MD5("username:password") or other similar variants, to see if you get a match.
• Is the password length limited ? Namely, if you set a 40-character password and cannot successfully authenticate by typing only the first 39 characters, then this means that all characters are important, and this implies that this really is password hashing, not encryption (the stored value is used to verify a password, but the password cannot be recovered from the stored value alone).

Answer 2

Edit: I just noticed a very cool script named hashID. The name pretty much describes it.

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Generally speaking, using experience to make educated guesses is how these things are done.

Here is a list with a very big number of hash outputs so that you know how each one looks and create signatures/patters or just optically verify.

• Online Hash Crack Hashes Generator
• InsidePro Software Forum > Hash Types (via Archive.org)

There are two main things you first pay attention to:

• the length of the hash (each hash function has a specific output length)
• the alphabet used (are all english letters? numbers 0-9 and A-F so hex? what special characters are there if any?)

Several password cracking programs (John the ripper for example) apply some pattern matching on the input to guess the algorithm used, but this only works on generic hashes. For example, if you take any hash output and rotate each letter by 1, most pattern matching schemes will fail.

Answer 3

What you have posted is 16 bytes (128 bits) of base 64 encoded data. The fact that it is base 64 encoded doesn't tell us much because base 64 is not an encryption/hashing algorithm it is a way to encode binary data into text. This means that this block includes one useful piece of information, namely that the output is 16 bytes long. We can compare this to the block size of commonly used schemes and figure out what it can't be. By far the most common schemes are:

• SHA-1 (160 bits)
• MD5 (128 bits)
• AES (128 bits)
• DES (64 bits)
• 3DES (64 bits)

The next thing we need to do is to look at other blocks of cipher text to figure out the answer to the following question:

• Are all cipher texts the same length, even for different input lengths?

If not all blocks are the same length then you aren't looking at a hashing algorithm, but an encryption one. Since the output will always be a multiple of the underlying block size the presence of a block that is not evenly divisible by 16 bytes would mean that it cant be AES and therefore must be DES or 3DES.

If you have the ability to put in a password and observe the output this can be determined very quickly. Just put in a 17 character password and look at the length. If its 16 bytes you have MD5, 20 bytes means SHA-1, 24 bytes means DES or 3DES, 32 bytes means AES.

Answer 4

If this is indeed a simple password hash, we might be able to use Google to crack it. Base64 is hard to search for, though, with all those slashes and plus signs, so let's first convert that hash into hexadecimal:

$ perl -MMIME::Base64 -le 'print unpack "H*", decode_base64 "WeJcFMQ/8+8QJ/w0hHh+0g=="'
59e25c14c43ff3ef1027fc3484787ed2

OK, now we can Google for it. At the moment, I'm getting only one hit, from md5this.com — although obviously there will quite soon be more, including this post.

Unfortunately (or perhaps fortunately, depending on your perspective), we're not lucky enough to actually find a preimage (the site currently lists this hash as "cracking..."), but the fact that it's on that list at all does strongly suggest that it's indeed an unsalted MD5 hash of a real password.

Answer 5

It depends upon the format - some protocols for storing encrypted text have a cleartext portion that defines how it's encrypted. From your example, I'm doubtful since the string you reference is so short that it looks like it's just the encrypted text.

I'd suggest a couple thoughts:

• The "==" on the end would definitely be padding, so don't include that in any decryption attempts.

• You may be dealing with a hash or a salted hash, rather than encryption. In that case, trying to "decrypt" the data won't work - you need to match passwords by using the same hash and/or salt value that was used originally. There is no way with a salted password to get the original value.

• Your absolute best bet is to get a copy of the code that is used to store the passwords. Somewhere in there, the passwords are undergoing a cryptographic operation. Find the code to learn what's happening here. 9 times out of 10, they are using some sort of API for the hashing/salting/encryption and you can imitate or reverse it using the same API.

Answer 6

Encoding can generally be guessed at. For example, the string you posted in your question is Base64 encoded. The equals signs are padding in the Base64 scheme. That's something I know on-sight from experience.

If you gave me a string that was encrypted, I may be able to tell you the encoding but I can't tell you the algorithm used to encrypt it unless some sort of metadata is available. The reason is this: encryption algorithms work by producing what appears to be random data. If I encrypted two sentences each with two ciphers (four outputs), you would be unable to tell me with any confidence which ciphertext belonged to which cipher unless you decrypted it or broke the cipher.

In regards to your specific instance, passwords are usually hashed. That means you can't recover the password from the hash, but you can test to see if the hash matches for the password. In that regard, @john's answer is golden. If you can input a password that you know and then try common schemes against it, you can learn what the hash used is.

Answer 7

This is very weak security on all fronts! The plaintext is P4$$w0rdP4$$w0rd and it's encrypted using XOR encryption, with the key CdZ4MLMPgYtAE9gQ80gMtg==. This produces the ciphertext posted by the OP above, WeJcFMQ/8+8QJ/w0hHh+0g==.

To verify:

First, use xxd to get the underlying binary of the plaintext:

echo -n 'P4$$w0rdP4$$w0rd' | xxd -b -c16

This produces:

01010000 00110100 00100100 00100100 01110111 00110000 01110010 01100100 01010000 00110100 00100100 00100100 01110111 00110000 01110010 01100100

Next, base64-decode the key and use xxd to get the underlying binary of the key:

echo -n 'CdZ4MLMPgYtAE9gQ80gMtg==' | base64 -d | xxd -b -c16

This produces:

00001001 11010110 01111000 00110000 10110011 00001111 10000001 10001011 01000000 00010011 11011000 00010000 11110011 01001000 00001100 10110110

Now, XOR the two binary strings:

01010000 00110100 00100100 00100100 01110111 00110000 01110010 01100100 01010000 00110100 00100100 00100100 01110111 00110000 01110010 01100100  (plaintext)
[XOR]
00001001 11010110 01111000 00110000 10110011 00001111 10000001 10001011 01000000 00010011 11011000 00010000 11110011 01001000 00001100 10110110  (key)
-----------------------------------------------------------------------------------------------------------------------------------------------
01011001 11100010 01011100 00010100 11000100 00111111 11110011 11101111 00010000 00100111 11111100 00110100 10000100 01111000 01111110 11010010  (ciphertext)

Finally, use bc, xxd, and base64 to convert the binary ciphertext to base64:

echo "obase=16; ibase=2; 01011001111000100101110000010100110001000011111111110011111011110001000000100111111111000011010010000100011110000111111011010010" | bc | xxd -p -r | base64

This produces WeJcFMQ/8+8QJ/w0hHh+0g==, which is the ciphertext posted by the OP in the question above.

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I apologize if this answer seems contrived. Admittedly, it is. Questions similar to this, where the poster provides only some ciphertext, and asks for some insight as to how that ciphertext could have been produced, seem come up quite frequently on security.stackexchange.com; and this question is often referenced as a duplicate to those. The point of this answer is to illustrate that questions of this nature are unanswerable, because there are infinite solutions to these types of questions.

Answer 8

The only way is to guess. With experience, guess works will be more correct.

For example: Based on length of output: MD5 output is 128 bits, or 16 bytes, SHA1 output is 160 bits, or 20 bytes. Based on charset of output: BASE64 produces output with printable characters.

At the end of the day, it's the try-and-error approach that teaches you how.

Answer 9

The only way is when there's some metadata that tells you. For instance, I've been working with PDFs lately, and the format includes a dictionary containing the filter, algorithm, key size etc. But if all you've got is the ciphertext, then all you've got is some opaque blob of data.