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8h
revised Why does applying 56-bit DES twice only give 57 bits of security?
Better title, improved formatting
10h
comment Why is triple-DES using three different keys vulnerable to a meet-in-the-middle-attack?
Let me just see if I understand this correctly. The absolute security of a two-key 3DES EDE (or said differently, three-key EDE where K1 == K3) scheme is very near identical to that of a three-independent-keys 3DES EDE scheme; the three-key scheme is only considered "worse" because we'd expect the three-key scheme to, in an ideal world, provide three times the algorithm's key length worth of security, not twice the algorithm's key length, so in the three-independent-keys scheme we aren't getting our full 168 bits worth?
10h
suggested approved edit on Why does applying 56-bit DES twice only give 57 bits of security?
Mar
31
awarded  Citizen Patrol
Oct
5
awarded  Editor
Oct
5
revised How is XOR used for encryption?
Copy editing
Oct
5
suggested approved edit on How is XOR used for encryption?
Aug
1
awarded  Commentator
Dec
17
awarded  Scholar
Dec
17
accepted What is the GnuPG process for going from a passphrase to a symmetric key?
Dec
16
comment What is the GnuPG process for going from a passphrase to a symmetric key?
So if I understand you and the RFC correctly, the user-provided passphrase is basically concatenated as many times as necessary to achieve the string length defined in RFC 4880 § 3.7.1.3, hashed according to the selected S2K algorithm, and then as stated in 3.7.1.1 the selected encryption algorithm's key length number of bits is taken out of the resultant hash value. That data is then used as the key to encrypt the ESK packet (5.3, holding a random session key which is used to encrypt the payload), stated in 3.7.2.2. Would you say that this interpretation agrees with yours?
Dec
14
awarded  Student
Dec
14
asked What is the GnuPG process for going from a passphrase to a symmetric key?
Sep
20
comment Why not the one-time pad with pseudo-number generator
@CodesInChaos That's what 1224Z is about (I ran out of space in 1223Z): you are able to (for some definition thereof) securely transmit data now but want to securely transmit data later. In such a case, an OTP can be useful. But try AES-256, and if that isn't enough, forget about 3DES and rather try 3AES256; even triple AES-256 will be orders of magnitude more practical from a key management perspective than an OTP. The true RNG in this answer means the pad must be distributed ahead of time, it cannot be generated simultaneously by the recipient, which breaks the OP's implied assumption.
Sep
19
comment How would I make a secret notation alphabet more secure?
What you have is likely a substitution and transposition cipher. To make it harder to decode, for starters you can use a code book (for common bi- and trigrams, perhaps) and/or shift the key by some amount for each character or group. But it'll still almost certainly be trivial to decode for someone who tries. What you'd almost certainly want to do is remove the statistical significance of the various glyphs, which even with transposition can give vital clues as to the content of the message. Leaving out punctuation only works insofar as it obscures the structure of the plaintext.
Sep
19
comment Why not the one-time pad with pseudo-number generator
@Gilles I did comment somewhere (might have been IT Security) that OTPs have a use where you have a secure channel now but need to transmit provably secure messages later. But even then, you still at the very least have the problem of storing the pad until it's needed.
Sep
19
comment Why not the one-time pad with pseudo-number generator
@Gilles Exactly. If you have a secure channel to transmit the OTP, why not just use that channel to transmit the message in the first place? If on the other hand the second channel is no more secure than the first, you have solved nothing from a confidentiality point of view - anyone who can eavesdrop on one channel can also eavesdrop on the other. It may pose a problem to a garden variety attacker, but not to a determined adversary - and to protect against a garden variety attacker, a reasonable mode of AES-256 is more than enough and requires only the secure distribution of 32 bytes of key.
Sep
19
awarded  Supporter
Sep
19
comment Why not the one-time pad with pseudo-number generator
How would the recipient decrypt the data then? (Not my downvote.)
Sep
6
comment Who uses Dual_EC_DRBG?
Link-only answers are discouraged on Stack Exchange. It's best to summarize the key points made in the linked page in the answer itself, so that if the link ever becomes invalid for any reason the answer will still be useful.