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bio website github.com/CodesInChaos
location Frankfurt, Germany
age
visits member for 3 years
seen 9 hours ago

Jan
10
comment Is it possible to break a hash-based block cipher?
A block cipher is a keyed permutation of a single block. So this is no block-cipher, and using it in CBC is a nonsensical operation. It looks like you're using a hash function in CTR mode, to construct a stream cipher.
Jan
9
revised Examples of applications that use the Schnorr digital signature?
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Jan
9
revised Examples of applications that use the Schnorr digital signature?
edited body
Jan
9
answered Examples of applications that use the Schnorr digital signature?
Jan
9
revised Using same keypair for Diffie-Hellman and signing
deleted 33 characters in body
Jan
9
comment How can we determine if two discrete logarithms are equal?
I believe there are some groups in which the decisional DH problem is easy, but the computational DH problem is hard. These are useful for some unusual protocols.
Jan
9
comment Examples of applications that use the Schnorr digital signature?
Tahoe-LAFS, Cryptosphere and me plan to use Ed25519. Bitcoin discussed it, but they probably won't.
Jan
9
comment Examples of applications that use the Schnorr digital signature?
I don't know anybody who uses it yet, but some are planning to use Ed25519, which is based on Schnorr.
Jan
9
revised What is “Blinding” used for in cryptography?
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Jan
9
comment What is “Blinding” used for in cryptography?
1) Blind RSA signatures 2) Avoiding certain side-channel attacks by working on blinded data
Jan
8
comment Using CBC with a fixed IV and a random first plaintext block
+1 for the NIST quote
Jan
8
comment Why is RSA usually limited to messages up to 1 block
One could probably construct modes that only need randomness for the first block in an IV like manned when using a chained mode. But there is little reason to put in the effort to design such a mode that still will be much worse than AES.
Jan
8
comment Deriving Keys for Symmetric Encryption and Authentication
I'd use HKDF for the key derivation
Jan
7
revised Is 512-bit RSA still safe for signature generation?
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Jan
7
answered Is 512-bit RSA still safe for signature generation?
Jan
7
comment Why not use CBC, not send IV, and assume first plaintext block is garbage?
This question is very similar to Using CBC with fixed IV
Jan
7
comment Where can I learn basic cryptography to know more about passwords and Bitcoin?
@superuser In this respect pretty much any hash used in practice is good(even MD5). Only really bad homebrew hashes would be vulnerable to that. Using fast hashes or not salting are the two common issues. | PS. you can't use line breaks in comments, only in questions and answers.
Jan
7
answered Where can I learn basic cryptography to know more about passwords and Bitcoin?
Jan
7
comment Why does WPA-PSK not use Diffie-Hellman key exchange?
They only have a weak long term secret in common. Those aren't good keys for encryption.
Jan
7
comment Why does WPA-PSK not use Diffie-Hellman key exchange?
@Thomas I disagree for several reasons. 1) Password entropy is often low, so using them only for authentication and not for confidentiality seems appropriate 2) Forward secrecy 3) All users who share a WiFi network can read each other's traffic. With a well constructed protocol an attack would have to be active, and one might even bind to the access spot's key, giving a warning when it changes.