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Jan
28
comment What is a smart card?
You have provided admirably plenty valuable informations. In a particular product: bsi.bund.de/SharedDocs/Downloads/DE/BSI/Zertifizierung/… there are stated: "The TOE provides full on-chip encryption covering the complete core, busses, memories and cryptographic co-processors leaving no plaintext on the chip." "No data in plain are handled anywhere on the TOE and thus also the two CPUs compute entirely masked and in addition dynamic mask changes are applied." Wouldn't that mean that homomorphic computations are being done there?
Jan
26
comment Cryptographic Symmetric Stream Cipher
What is the point of requiring two "independent" computers? Wouldn't one computer be sufficient in any case?
Jan
26
answered Any efficient text-based steganographic schemes?
Jan
25
comment Any efficient text-based steganographic schemes?
Concerning (2): With careful examination of inserted spaces at line-end etc., the warden can easily detect these. Thus they are insecure IMHO. I have myself designed a scheme using the number of words per line to transmit one stego-bit (EMAILSTEGANO in s13.zetaboards.com/crypto) but its stego-bit rate is very low. Much higher stego-bit rates would IMHO be badly needed in certain practical situations. I'll be very interested in schemes using the 3rd method you listed under (3) above. Do you happen to have a few references to them?
Jan
24
answered What is a block cipher?
Jan
23
comment Any efficient text-based steganographic schemes?
Right. But my previous comment was for encrypted stego bits. (Encryption is a necessity if a stego scheme is to be of any non-trivial usage in practice nowadays at least.)
Jan
23
comment Any efficient text-based steganographic schemes?
I doubt your point of 'user friendly'. Could you give some convincing examples or references containing such?
Jan
21
asked Any efficient text-based steganographic schemes?
Jan
20
asked Any implication of a Yale result to security of quantum cryptology?
Jan
16
awarded  Critic
Dec
10
comment Deriving Keys for Symmetric Encryption and Authentication
@PaŭloEbermann: For "definition" you are certainly right. But the security aspect is IMHO the same, thus establishing the usefulness of the idea I mentioned. Note that if a sequence obtained from counter mode (via increasing by 1) can be securely used, then an arbitray sub-sequence, say consisting of the 5-th, 24-th, 88-th, 109-th etc. of the sequence, should also be secure.
Dec
10
comment Deriving Keys for Symmetric Encryption and Authentication
I remember to have mentioned the method of deriving keys from a master key via a block cipher in counter mode many years ago in another forum, thinking though even at that time that the idea very probably was old and well known. Recently however in discussions elsewhere I got the impression that it may not have been widely known, probably due to lack of mention in the literature. The idea of having a hierarchy of master keys to derive session keys dynamically was mentioned in my code JADE in s13.zetaboards.com/Crypto/index
Dec
10
comment Deriving Keys for Symmetric Encryption and Authentication
@PaŭloEbermann: Right. For counter mode the key is secret as usual. The plaintext part is an arbitrary numerical value, normally successsively counted up by 1 (or by any amount), but that input could just as well form any arbitrary sequence of values (e.g. containing time and message serial numbers, etc. etc., arbeit not necessarily to be very strongly guarded for security resaons).
Dec
9
answered Deriving Keys for Symmetric Encryption and Authentication
Oct
9
awarded  Teacher
Oct
9
answered One time pad key exchange
Oct
3
awarded  Commentator
Oct
3
comment How could block encryption in counter mode be secure from viewpoint of entropy?
@PaŭloEbermann: But estimates based on computing power could be difficult/problematic due to uncertainty in predictions of future developments either in software (methods of computation) or in hardware, if the secrecy has to be maintained for quite a long time. I vaguely remember to have seen a paper where Rivest made such a claim for a RSA key size that is way smaller than what is currently considered to be appropriate.
Oct
1
awarded  Student
Oct
1
comment How could block encryption in counter mode be secure from viewpoint of entropy?
Ok, but then how much security measures does one need in order to protect against a "practical" adversary? That's a rather fuzzy and hard to determine matter, isn't it?