11
votes
What is DES-EDE3-CBC?
At least in the context of PKCS#5 (which is commonly seen through the encryption of PEM files), DES-EDE3-CBC is Triple DES with three keys, used in CBC mode, with unspecified padding.
Yes, “EDE” means ...
4
votes
(DES) What is the probability that two keys (k1, k2) produce the same ciphertext given the same plaintext?
It depends on what you mean. There are $2^{56}$ different DES keys and so if $k_1$ and $k_2$ are both chosen uniformly and independently at random, then there is a $2^{-56}$ chance that they are the ...
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3
votes
Accepted
Why do we encrypt then decrypt then encrypt data with different keys?
This is usually called "RetailMAC" as it is mainly used by commercial applications. Sometimes it is also referred to as ISO7816-4D2 MAC, even though ISO/IEC 7816-4 not the place where it is ...
- 90.2k
3
votes
(DES) What is the probability that two keys (k1, k2) produce the same ciphertext given the same plaintext?
Let $DES(p,k)$ be modeled by the pseudorandom permutation $\pi_{k}:\{0,1\}^{64}\rightarrow \{0,1\}^{64}.$ Then
$$
DES(p,k_1)=DES(p,k_2) \Leftrightarrow \pi_{k_2}^{-1}(\pi_{k_1}(p))=p.
$$
Since $\pi_{...
- 20k
2
votes
Accepted
2DES has an identity key - clarification
Why is that so?
It's a property of DES, known as 'weak keys'. What DES does during decryption is generate the same set of 16 subkeys as it does during encryption, however it processes them in the ...
- 140k
2
votes
DES initial key generation
In symmetric cryptography, including DES, the standard assumption is that the key is randomly and secretly selected among the set of valid keys.
In DES, there are three variations of the set of valid ...
- 134k
2
votes
DES initial key generation
In any cipher system the key is required to be generated by a uniformly random process, and be equidistributed, each bit equally likely to be $0$ vs $1$ as well as independent of other bits.
...
- 20k
2
votes
What is DES-EDE3-CBC?
My guess is the same as that in the question: DES-EDE3-CBC most likely stands for
The block cipher TDEA (aka 3DES) with keying option 1 as defined by FIPS 46-3. This essentially is the DEA (aka DES) ...
- 134k
2
votes
Why do we encrypt then decrypt then encrypt data with different keys?
If symetric cryptography is about using the same key for encryption and decryption, then what's the logic behind decrypting data with a different key than the one used to encrypt it?
Operations ...
- 309
1
vote
Accepted
DES attack with known partial plaintext
You don't have things quite right; I suspect focusing on the DES block size is confusing you.
Here is the way I found useful when addressing this situation: we model our decryption such that if we ...
- 140k
1
vote
How to find fixed points for DES weak keys
In 1987 Judy H. Moore and Gustavus J. Simmons proved that for each of the four DES weak keys there are exactly $2^{32}$ fixed points. Fixed points where all round keys are different was an open ...
1
vote
Accepted
How is DES used with CBC?
CBC is a mode of operation, and is defined for an arbitrary block cipher, which can be DES, AES or whatever you like. See Wikipedia for example.
A block cipher typically processes 64 bit or 128 bit ...
- 20k
1
vote
Attack on AES/DES
A canonical question on this site lists several models against which a cipher must be secure in modern days. In essence, if used with a proper mode of operation, the premise that the frequence of ...
- 8,291
1
vote
Accepted
Equivalance of encryption and decryption in DES under bruteforce
because if DEC and ENC are equivalent, then $DEC_{k4}(DEC_{k5}(M))$ will in fact cancel each other.
Actually, just because DEC and ENC are similar (identical except for subkey generation) doesn't ...
- 140k
1
vote
What is the importance of superencryption?
If you're using a strong cipher like AES, there is no need to cascade it. The only reason to cascade is if the cipher has a small key size and silly federal regulations demand that you keep using it. ...
- 14.9k
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