The author seems to think that second preimage attack and collission attack are the same. They’re not.

Second preimage attack: Given a hash function H and an input X find Y so that H(X)=H(Y) and X!=Y.

Collission attack: Given only a hash function find X, Y so that H(X) = H(Y).

This is a major difference. There are plenty of hash functions that are vulnerable to the second, but not the first (most notably MD5, SHA1).

My bad, thank you for pointing that out! I’ll update the post.

Is the birthday paradox correct in this case? We’re not looking for any two coins the same colour, we’re looking for a coin the same colour as the one we already have?

I think you’re right. The current metaphor describes a second preimage attack. I’ll update the post. Thank you.

Nice post Jeff.

2^256 is about 10^77, which happens to be an estimate for the number of atoms in the universe.

I really like your blog layout. Have you published the code?

Thanks! It’s using this Hugo theme https://github.com/htr3n/hyde-hyde with some tiny modifications.

The author seems to think that second preimage attack and collission attack are the same. They’re not.

Second preimage attack: Given a hash function H and an input X find Y so that H(X)=H(Y) and X!=Y.

Collission attack: Given only a hash function find X, Y so that H(X) = H(Y).

This is a major difference. There are plenty of hash functions that are vulnerable to the second, but not the first (most notably MD5, SHA1).

My bad, thank you for pointing that out! I’ll update the post.

Is the birthday paradox correct in this case? We’re not looking for any two coins the same colour, we’re looking for a coin the same colour as the one we already have?

I think you’re right. The current metaphor describes a second preimage attack. I’ll update the post. Thank you.

Nice post Jeff.

2^256 is about 10^77, which happens to be an estimate for the number of atoms in the universe.

I really like your blog layout. Have you published the code?

Thanks! It’s using this Hugo theme https://github.com/htr3n/hyde-hyde with some tiny modifications.