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location Netherlands
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visits member for 2 years, 11 months
seen 3 hours ago

Java and security expert with over 10 years of experience with the language and with the practical application of cryptographic protocols - including the design of protocols within international standardization bodies. Creator of a heavily used common criteria certified product. Over 30 years of experience with computers. Likes kids, cats, reading, movies and several sports.


6h
comment Secure way to derive separate encryption and MAC keys from a single master key?
@RickyDemer Hmm, hard to put in words, tried "if larger input is allowed".
6h
revised Secure way to derive separate encryption and MAC keys from a single master key?
deleted 3 characters in body
8h
revised Does the size of a SSH ECDSA key determine the hash algorithm?
added 84 characters in body
9h
revised Does the size of a SSH ECDSA key determine the hash algorithm?
edited title
9h
comment Does the size of a SSH ECDSA key determine the hash algorithm?
@otus I was wondering, so I provided the answer myself and flagged it for transfer to IT security.
9h
answered Does the size of a SSH ECDSA key determine the hash algorithm?
9h
revised Security of KDF1 and KDF2 (hash based KDF's)
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11h
comment Secure way to derive separate encryption and MAC keys from a single master key?
@RichieFrame Let us agree that it is fast (especially on 64 bit) and secure, but that it doesn't scale well :)
11h
answered What can be learned from the ciphertext of LibSodium's crypto_box_detached()?
12h
comment Secure way to derive separate encryption and MAC keys from a single master key?
I toned that down somewhat and expanded the answer. I based that assumption on that of Ilmari who supplied the other answer. Nevertheless, KDF1/2 are used in practice and I've not seen any attacks on it either.
12h
revised What can be learned from the ciphertext of LibSodium's crypto_box_detached()?
added 76 characters in body
12h
revised Secure way to derive separate encryption and MAC keys from a single master key?
toned down the "are secure" into "should be secure", created an extended answer
12h
revised Security of KDF1 and KDF2 (hash based KDF's)
deleted 73 characters in body; edited tags
12h
revised Secure way to derive separate encryption and MAC keys from a single master key?
toned down the "are secure" into "should be secure", created an extended answer
23h
comment Operation which needs much computing power to be created, but just a little to be solved?
I'd like to answer, but I've got a sudoku to solve.
1d
comment HMAC_DRBG Generate Process: requesting N bytes at once different from requesting N bytes in total?
Whoops, waited a bit too long for other possible answers, sorry about that :)
1d
accepted HMAC_DRBG Generate Process: requesting N bytes at once different from requesting N bytes in total?
1d
comment What are the advantages of Certificate Authority and Key Distribution Center over each other?
It depends on what you want to achieve I guess. Wikipedia defines "In cryptography, a key distribution center (KDC) is part of a cryptosystem intended to reduce the risks inherent in exchanging keys. KDCs often operate in systems within which some users may have permission to use certain services at some times and not at others." That's different from a CA, which simply signs certificate requests, giving certificates with public keys that are available for (usually) a longer period of time. So there are differences, what is unclear?
1d
comment Secure way to derive separate encryption and MAC keys from a single master key?
Yes that's kind of possible, but scrypt was created to do key stretching using a work factor (and, in the case of scrypt, a large internal state). Usually it is possible to use a Password Based Key Derivation Function (PBKDF) instead of a Key Based Key Derivation Function (KBKDF), which is what is required.
1d
comment Secure way to derive separate encryption and MAC keys from a single master key?
@RichieFrame That's likely secure and likely the fastest method as well, but it doesn't scale with the size of the keys, hash or number of keys that required. Using a well defined KDF should be preferred IMHO.