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Mar
19
comment Can double-encrypting be easier to break then either algorithm on its own?
ROT13 is "real encryption", providing you consider a Caesar shift to be "real encryption". In general, a double encryption with Caesar shifts will be a null operation if the two keys (= shifts) chosen add up to a multiple of 26. With ROT13: 13 + 13 = 26.
Jan
21
awarded  Yearling
Jan
10
comment Steganographic embedding of an RSA-encrypted message into an image
If the message is a known, fixed length, then it is better to use random LSBs to fill up the image. That leaks less information to an attacker. If the message is variable length, then either encode the length as the first 16 bits of the message -- there is room -- or pad with 1000 ... 000 which can be cleanly removed. Zero padding isn't; the message may end with a 0 bit.
Jun
22
awarded  Caucus
Jun
22
comment How can I start the following crypto project?
This is a big question. Break it up into smaller chunks. Start work on one chunk. If you get stuck, ask again with a specific question about the particular chunk you are working on. Remember that you can ask your instructor for clarification or assistance as well as here. Repeat until you have completed all the chunks.
Jun
22
answered Which symmetric cipher is best for studying?
Jun
11
answered simple algorithm to encrypt/decrypt a text file
Jun
7
awarded  Enlightened
Jun
7
awarded  Nice Answer
May
1
comment Is it safe to derive two different keys with the same password and key derivation function using two different salts?
@fgrieu Agreed. This is crypto, so belt and braces (I am English) are often the default.
Apr
30
answered Is it fair to assume that SHA1 collisions won't occur on a set of <100k strings
Apr
30
awarded  Commentator
Apr
30
comment Is it safe to derive two different keys with the same password and key derivation function using two different salts?
In this situation I would tend to differentiate the keys by adding "-KEY1" and "-KEY2" to the initial master password before input to the KDF, YMMV.
Sep
24
awarded  Autobiographer
Sep
13
answered How hard to break a cipher if it has a different key for each word?
Apr
19
comment One time pad: why is it useless in practice?
Since the pad is at least the same size as the message, then if you have a secure channel to transmit the pad, you can often use the same channel to transmit the message itself, and not bother with the pad at all. OTPs are sometimes used when the pad transmission is simple (hand a memory stick to your spy) but the later message transmission is difficult (transmit the secret enemy plans).
Apr
15
comment Positioning of keys in encrypted text
Are you sure that you are not confusing the IV (Initialization Vector) with the key? It is common to prepend the IV to the cyphertext. It is an obvious error to prepend the key to the cyphertext.
Nov
30
awarded  Yearling
Nov
30
awarded  Yearling
Nov
28
awarded  Nice Answer