# Questions tagged [constants]

Fixed, more or less arbitrary parameter values that appear in the definitions of cryptographic schemes, such as fixed initialization vectors for hash functions or S-box tables for block ciphers.

18 questions
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### How complex must round constants be to resist slide attacks?

A key schedule that generates round keys by XORing a round constant with the key is linear and can be vulnerable to related key attacks, but let's ignore that for now. Constants are necessary to avoid ...
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### Early propagation of carries in the BLAKE hash function

The BLAKE paper uses round constants derived from $\pi$ to improve diffusion, even if the additions modulo $2^{32}$ are replaced with bitwise XOR when processing a null message and null initial state: ...
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### Using non-standard constants for SHA-256

For SHA-256, FIPS 180-4 states the following on the constants: These words represent the first thirty-two bits of the fractional parts of the cube roots of the first sixty-four prime numbers. If ...
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### Amateur question: Constant two way cryptography

First of all, I would like to tell you guys that I'm a complete noob at cryptography in general, so please pardon any dumb stuff I may say. Well, I have used a lot of cryptography libraries in a ...
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### Is there a standard, or widely accepted convention, for magic constants in crypto software?

Inspired by Magic "Nothing Up My Sleeve" Numbers - Computerphile - YouTube [5:31]. If you just need a constant to begin your algorithm, and the value of that constant isn't important, why not have a ...
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### Origin of the SHA-224 initial hash value?

At the start of each of the SHA-0 through -2 algorithms, the initial state is set to certain constants. I'm curious where the initialization values in SHA-224 are from. MD5's initial values are ...
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### How Elliptic Curve equation is chosen?

We all know the basic equation of Elliptic Curve is $y^2 \equiv x^3 + ax + b \pmod p$ How the value of the constants $a$ and $b$ are chosen? Suppose $\mathbb P\ni p \approx 2^{256}$ then what ...
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### How constant value 0x63 in affine transformation is chosen or generated while AES Substitution Box is formed?

Me and one of my friends are working on AES algorithm. We have understood how multiplicative inverse table is generated. Rijndael AES algorithm shows us how S-Box is generated through the affine ...
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### How are the IVs of SHA512/256 and SHA512/224 calculated?

This seems odd to me, because there are a lot of resources out there saying that the initializer values of SHA512 and SHA384 are the first 64 bits of the fractional parts of the square roots of prime ...
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### Can homomorphic operations on many different ciphertexts be multiplied by a same constant?

Assume Alice encrypts messages $m_1$,...,$m_n$ using secret keys $k_1$,...,$k_n$ on a homomorphic encryption scheme (BHHO), so she would get $c_1=Enc_{k_1}(m_1)$,...,$c_n=Enc_{k_n}(m_n)$. Then Alice ...
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### Are the MD5 constants an S-Box?

I noticed that several hash algorithms, in this case MD5, defines some constants. MD5 defines 64 constant values (the shift count per round) which also gets expand (via sine) to a summand for a ...
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### How is the MD2 hash function S-table constructed from Pi?

For fun, I'm learning more about cryptography and hashing. I'm implementing the MD2 hash function following RFC 1319 (http://tools.ietf.org/html/rfc1319). I'll preface by saying I know there are ...