# Tag Info

13

Well, the standard answer is to preserve compatibility with DES; a hardware circuit that implemented 3DES (with EDE) could also be used to do DES as well (by, say, making all three subkeys the same). Now, there is one slight problem with this straightforward argument; 3DES (EEE, that is, with three encrypt operations) would have this property as well; if we ...

10

The main difference is that with two 56 bit keys the maximal security level is 112 bit, and thus an attack that has a cost of $2^{112}$ operations is no attack, whereas for three 56 bit keys the maximal security level is 168 bits, and an attack that has a cost of $2^{112}$ operations counts as an attack. This means that two-key 3DES is still a bit weaker ...

8

DES has a block size of 8 bytes. Two blocks therefore come to 16 bytes. It looks like Adbobe were encrypting passwords using two blocks of 3-DES in ECB mode. Because all these passwords are eight bytes long, the second block is empty and is just filled with zeros. The second block gets started at all because of the string-terminating NUL character at the ...

6

The article mentions that 3-DES was used to encrypt these passwords in ECB mode. DES has a 64-bit/8-byte block. So let's say you use ECB to encrypt a nine byte password. The first 8-bytes are encrypted using ECB. So far so good. But what happens when we come to the ninth byte? Well we're now in a new block but only the first byte is populated with any ...

5

<------------- key -------------> <-- plaintext -> <- ciphertext -> E62CABB93D1F3BDC 524FDF91A279C297 DD16B3D004069AB3 8ADDBD2290E565CE B619F870574A9E80 DAE6AB34C22CD626 058B92A4B28FB4EB A53DDC6B3098008F 6132C42C3E5E94EF 7A5152BF19AB739D 91993307EFBFB13C D13105386083E517 0245EAFE62DF92BF E319C29E9E2C3EA1 58BAA732CF5DBD77 EF37441D1FE7B73A ...

5

Note: I'll disregard the base64 encoding in the following text; the base64 encoding does not change the properties of the generated ciphertext. What you are running into is padding together with ECB mode. This padding can be any static padding. Most common is PKCS#5 padding, but zero padding is also possible. It is not possible to test which padding is ...

4

The answer is: Why do the encrypted files always start with "Salted__" ("U2FsdGVkX1" in base64)? Isn't giving away information like this insecure? The encrypted files must always start with "Salted_" to interoperate with OpenSSL. OpenSSL expects this. The 8 bytes that spell "Salted_" are always immediately followed by another random 8 bytes of salt. ...

4

Assuming the mod 11 check digit is among 0123456789X, disclosing it reduces the number of possible plaintexts among 8-digit numbers by a factor of about 11 (from 100000000 to about 9090909; exactly how much depends very slightly on the value of the check digit), thus reveals about $\log_2(11)$ bits of information about the plaintext, that is just a little ...

4

3DES is a block cipher which processes "blocks" of 64 bits. A block cipher is not sufficient to encrypt a message, defined as a sequence of potentially many bytes. Hence the use of a mode of operation which organizes things; this may imply some padding, and an Initialization Vector. TripleDESCryptoServiceProvider can do all that: you specify the key, the ...

3

If you're asking why the X9.31 rng was designed the way it was, rather than some other way, I'm not certain if anyone other than the original authors could say. The core design dates back to at least 1985 (it was included in X9.17), and it originally used DES (and was later upgraded to use 3DES). I suspect that the original authors would not have been ...

3

I do not understand how can we decrypt a cypher which was encrypted with $K_1$, with $K_2$. Triple DES essentially involves three encryptions on the plain text. First is using $K_1$, second using $K_2$, and third using $K_3$. Now one may argue that $K_2$ is not being used for encryption but decryption. Well, technically speaking, encryption and ...

3

Yes. The following papers should be exactly what you are looking for. The following paper shows that the answer is "Yes" and provides evidence that 3-key Triple DES is more secure than single DES: Code-Based Game-Playing Proofs and the Security of Triple Encryption. Mihir Bellare, Phillip Rogaway. IACR ePrint 2004/331. (Full version of a paper ...

2

To generate an IV securely for CBC mode, there are two obvious ways to do it (and both are cited by NIST): For each packet, select a nonce (the IPSec sequence number, padded out to 64 bits, works fine), encrypt that in ECB mode, and then use resulting ciphertext block as the IV. An equivalent way to do that is to take your 64 bit nonce, prepend that to ...

1

Knowing the check digit and the algorithm reduces the possible set of numbers from $10^8$ to under $10^6$. If there are other pieces of data available to the attacker (initials of the customer, ZIP code, etc.,) there could be enough information to correlate the customer with other sources of data without ever learning the account number. That may or may not ...

1

I think another reason for using the complicated construction which replaces $V$ after each production of a new $R$ is a (maybe implicit) requirement that the state of the PRNG should not allow recovering previous outputs. For a block cipher in CTR mode, recovering previous outputs is easy, as you still have all the input available, or easily ...

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