# Tag Info

5

TL;DR: the official $2^{80}$-something theoretical security of 2-Key Triple DES w.r.t. key search¹ is still practically good enough in most of its many uses in 2020; but security authorities rightly do not condone it in new applications. "3DES when $K_1=K_3$" is formally known as TDEA keying option 2 in FIPS 46-3 or 2TDEA or 2-Key Triple DES. It ...

3

If K1 = K3 and K1 and K2 are independent, your key length is 112 bits ($2*56$), but due to meet-in-the-middle attack, you have only 80 bits of security. Note: don't use 3DES and any other 64-bit block ciphers

3

First of all, 2DES is $$\textrm{ciphertext} = E_{K_1}(D_{K_2}(E_{K_1}(\textrm{plaintext})))$$ The below from 19 September 2020 on the Bitcoin mining, Bitcoin mining is based on SHA256d calculations. All in all, ASICs, FPGAs, GPUs, and CPUs. \begin{array} {|l|c|c|c|c|}\hline & \text{in a second} & \text{in a hour} & \text{in a day} & \text{...

2

When two of the three keys with 3DES are the same, you are using a 2*56-bit keyspace that would need to be brute forced. So, when K1=K3, the brute force difficulty will be 2^112. As @hypatia points out though, a meet-in-the-middle attack exists though so you could run an attack in 2^80 time, which is faster than brute force. Wikipedia has some more details ...

2

3DES What is described here is not 3DES (Triple DES or TDES and officially the Triple Data Encryption Algorithm (TDEA or Triple DEA)). Let us call the $E$ as DES encryption and $D$ as DES decryption. Then we can write 3DES encryption as $$E(k_3,D(k_2,E(k_1,message)))$$ with independent keys $k_1,k_2,k_3$. The provided security by 3DES with 3 key is not 192-...

1

My question is - when performing frequency analysis on such ciphers, do I input the hex ciphertext or do I need to transform it into text? How can I comment on that (based on letter frequency or bit occurrence)? First of all, what you are looking at is a hexadecimal representation of the ciphertext. The ciphertext itself does not consist of hexadecimals, it ...

1

A meet-in-the-middle attack basically halves the number of bits of the total key size, rounding up. So 3 and 4 both have 2x security and 5 and 6 block cipher encrypts provide 3x security of the original cipher. I think that this is the main misunderstanding of meet-in-the-middle attacks. The DES cipher itself is protected against meet-in-the-middle attacks, ...

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