crypt
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Why don't crypto-currencies use the Lamport signature scheme?
8 votes

The major issue will be size difference. The size of ECDSA in bitcoin is much less than the Lamport Signature. For ECDSA in bitcoin The public key is only 33 Bytes (1 byte for prefix, and 32 bytes ...

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Why is AES not a Feistel cipher?
8 votes

The simple answer is "Because its an SPN cipher". What is difference between Feistel and SPN? SPN operates on whole data in one round, where as Feistel divides data into N parts where N>=2 , then ...

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Active S-boxes for AES with 8x8 MDS matrix
Accepted answer
7 votes

It seems that using an 8x8 MDS will have 27 Active Sboxes after 4 Rounds(There may exist a trail shorter than 27). The image below shows the counting of active Sboxes. The Active and non-Active byte ...

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AES Decryption Process
4 votes

Reverse in a sense that every step done in encryption needs to be reversed. For Sbox, there is an Inverse Sbox. For MDS, there is an inverse of MDS(invMDS) such the multiplication of MDS and invMDS is ...

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Security of key schedule that only XORs a key with constants
4 votes

This key schedule is Totally Linear. If two Master Keys $MK$1 and $MK$2 have a difference of d, all the round keys will have difference of d with probability of 1. This makes the cipher vulnerable to ...

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AES key expansion for 192-bit
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4 votes

For 192 bit key(AES-192), there are 6 columns of 32 bit each i.e 4x6 Matrix. These 192bits of Master Key are shown as k0,k1...k5, i.e 6 words of 32 bit each. (See page 44 of Book "The Design of ...

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What affect does the permutation layer have on the avalanche effect?
3 votes

Permutation layer diffuses the small changes globally(tries to spread over the complete block). If permutation is not well thought out, then diffusion may be weak and changes may not spread ...

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Output of a Linear Shift Register given Plaintext and intial state
3 votes

If this can code can help you understanding the Linear Shift Register. (^ represents Exclusive OR) byte[] register = new byte[] { 0, 1, 0, 1 }; byte[] plain = new byte[] { 1, 0, 1, 0, ...

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How Unique is a "NeuralHash"?
2 votes

Apple's Neural Hash Algorithm has been reverse engineered and first collision has been reported.

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Robust stream cipher using AES encryption block
2 votes

You should use CTR mode. You will not need to have random IV every time, rather you will use incremental counter and set it to zero once you change the KEY. You should not encrypt more than ${2^{n/2}}$...

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Best method of converting a private key string into a 12 word mnemonic?
Accepted answer
2 votes

BIP 39 describes the implementation of a mnemonic code or mnemonic sentence -- a group of easy to remember words -- for the generation of deterministic wallets. Bitcoin private key is not stored in ...

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What is the difference between a Stream cipher and a Symmetric Encryption algorithm?
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2 votes

There are Three basic types of Encryption Symmetric. It uses same key for encryption and Decryption. Asymmetric. It uses two different keys(public and private) to encrypt and decrypt. Hash Functions....

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Difference between stream cipher and block cipher
2 votes

There are two basic types of Encryption Symmetric. It uses same key for encryption and Decryption. Asymmetric. It uses two different keys(public and private) to encrypt and decrypt. Block Cipher and ...

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About the Rijndael/AES sbox polynomial (subBytes)
2 votes

The image below shows the 30 irreducible polynomials for GF2^8. As an interesting factor it seems that 16 out of 30 has Hamming Weight of 4 (ignoring the MSB i.e x^8) and more interestingly 7 out of ...

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How can complexity be increased or decreased in AES?
2 votes

The Encryption is not likely Compression where one can choose Normal, High or Low or something from scale of 0-100 as you mentioned. If you really want to do it, you can think of it in two ways ...

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One-round feistel network (DES) attack
Accepted answer
1 votes

Since $$X' = F(X, k) = P(S(E(X) \oplus k ))$$ the value of key $K$ is an element of the set $$ \{V \oplus E(R_0): V \in S^{-1}(P^{-1}(Z)) \}$$ where $$Z = R_1 \oplus L_0$$ and $$ S^{-1}(P^{-1}(...

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Using round constants to thwart slide attacks
1 votes

Yes the different round keys help, but without the different round constants in key-schedule, all the rounds of key-schedule algorithm will be same. Thus these identical rounds may generate sliding ...

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Arbitrary length to multiple of block size
Accepted answer
1 votes

In CTR mode, Enc is done as CT = Enc(k,PT) = Enc(k,ctr) xor PT The decryption is similar to encryption except you XOR Cipertext(CT) instead of Plaintext(PT). PT = Dec(k,CT) = Enc(k,ctr) xor CT So ...

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What is the advantage of AES-GCM against CPA attack
1 votes

Section 8 of NIST SP 800-38D (Recommendation for Block Cipher Modes of peration: Galois/Counter Mode (GCM) and GMAC) deals with "UNIQUENESS REQUIREMENT ON IVS AND KEYS" the initial few lines state ...

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Is this function a secure PRF?
1 votes

Consider the Experiment where adversary sends m0 and m1 and gets encryption of either m0 or m1. Now he has to figure out he got encryption of m0 or m1. Adversary can proceed in following way ...

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Encrypted messaging web app design
1 votes

you should not encrypt plaintext message using public key. You may do following select a random 128, 192, or 256 bit key use a symmetric cipher to encrypt plaintext message using that key (you may ...

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RSA: How do I decrypt this?
1 votes

For efficient Encryption and decryption in RSA, method of “exponentiation by repeated squaring and multiplication” is used. Please read Section A(page 8) of the paper in which RSA was proposed. A ...

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Is building your own inefficient but secure cipher hard?
1 votes

Yes you may design, but a good one requires a lot of effort. Following steps may be helpful Pick up a standard cipher Study its specifications (understand it well) Start studying Cryptanalysis of ...

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Are there any advantages in using proprietary encryption?
1 votes

Keeping the Algorithm secure gives an advantage. Like GOST cipher was kept secret until its public release in 1994 whereas it was being used by Russians in 1970 too. So what we learn is, Algorithm ...

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Diffie-Hellman problem: is DH still secure if $g^{a^2}$ is known?
0 votes

It does not compromise DH security. Because computing $a$ from $g^a$ and $g^{a^2}$ is as hard as finding $a$ from $g^a$. So without knowledge of $a$ we cant compute $g^{ab}$ from just $g^a$ and $g^b$ ...

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How to find the right additive polynomial in inverse affine transformation in AES
Accepted answer
0 votes

The Affine Transformation for AES Sbox is given by Let M b the 8x8 binary matrix and C be the affine additive constant then B = M x A xor C --------------- (1) The straight forward reverse to this ...

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Name of specific cryptography property of XOR
Accepted answer
0 votes

XOR is a linear operation which is inverse of itself too. k1 $\oplus$ k1 = 0 It is also commutative. (k1 $\oplus$ k2) $\oplus$ k3 = k1 $\oplus$ (k2 $\oplus$ k3) Thats why you can decrypt the way ...

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How secure will this be against brute-force attacks?
0 votes

It all depends on your restriction of length of initial password. If your user is able to enter password of just 4 characters, then doing SHA1 etc is not going to add any entropy (in simple words the ...

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AES with shuffleBytes instead of shiftRows
Accepted answer
0 votes

AES ShiftRows operations ensures that each new column contains one byte from one of the 4 old columns. Thus it achieves Full diffusion in 2 rounds. You are right that there could have been other ...

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