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31 votes
Accepted

Why hashing twice?

A common rationale for hashing twice is to guard against the length-extension property of the hash (if it has that property, as many hashes before SHA-3 did). For SHA-256, this property allows to ...
fgrieu's user avatar
  • 142k
13 votes
Accepted

How to deal with collisions in Bitcoin addresses?

Cryptography (and real security in general) offer quantitative analysis of the security provided - Meaning, real security products will describe how long they will resist a certain class of attack. ...
Ella Rose's user avatar
  • 19.6k
9 votes

SHA256 and RIPEMD160 collisions

There are close to $2^{256}$ ECC keys while there are only $2^{160}$ 20-byte hashes, so the pidgeonhole principle shows that there exist collisions. On average there there are $2^{96}$ keys for each ...
CodesInChaos's user avatar
  • 24.9k
6 votes

How to deal with collisions in Bitcoin addresses?

In this application we don't care about attackers generating collisions with themselves. What we care about is. Two legitimate users inadvertently generating the same address. An attacker ...
Peter Green's user avatar
  • 1,594
3 votes
Accepted

Can you identify these cryptographic algorithmic symbols?

It is RIPEMD-160 and the paper describes them as; $f$ represents nonlinear functions at bit level: $exor, mux, -, mux, -$ and varies with rounds; $f(j, x, y, z) = x ⊕ y ⊕ z \quad \quad \quad \quad \...
kelalaka's user avatar
  • 48.7k
2 votes

HMAC-Ripemd-160 in TrueCrypt

The use of RIPEMD-160 is not a cause for concern. It's the relatively small number of PBKDF2 iterations which is problematic. More than a decade ago, the minimum recommended number of iterations was ...
forest's user avatar
  • 15.3k
2 votes
Accepted

Sane implementations of Bitcoin cryptography routines w.r.t. side-channel attacks

Is there a "sane" implementation of the algorithms used by bitcoin? e.g. are there high-quality implementations available that incorporate defenses against side channel attacks? libsecp256k1 Does ...
Squeamish Ossifrage's user avatar
2 votes
Accepted

Are there alternative ways to decrypt the public key to the public address

The "public address" is not a standard cryptographic notion (except perhaps in some subfield like cryptocurrency), and no context is given. That makes the most sensible way to rephrase the ...
fgrieu's user avatar
  • 142k
1 vote

Can you identify these cryptographic algorithmic symbols?

I don't know of a glossary for symbols on these diagrams, however in this case: $f$ is some sbox, that is, some lookup table (and whose details must be given somewhere else in the document where this ...
poncho's user avatar
  • 148k
1 vote

Why is a 1 added after the message input and before adding padding zeros (if necessary) when using SHA256 or RIPEMD160?

If you look at the Wikipedia on padding article page, you will see many different ideas. The main problem when designing a padding, firstly, one has to consider how to eliminate the padding correctly, ...
kelalaka's user avatar
  • 48.7k
1 vote

Long Term Security of Truecrypt's hash function?

Unlike the ciphers, the hash algorithm is not used directly to protect your data. Its only purpose is to take your ASCII passphrase and mix it up, shrinking or expanding it to the size required by the ...
forest's user avatar
  • 15.3k

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