Thomas
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 Apr30 comment How do decryption algorithms determine whether your attempted passphrase is correct? Did you see this question: crypto.stackexchange.com/questions/5921/… Apr17 comment Security of permutation cipher Arh.. ok. Now I see. Apr17 comment Security of permutation cipher Yes, I think that makes sense now. So you are saying the same as @fgrieu in this comment above? So one can't recover the entire plain text, but will be able to recover some. Apr16 comment Security of permutation cipher @rath: I am not sure that I understand. So in a sense the key consists of $sigma_1, \dots , \sigma_n$. It is assumed that these permutations are constructed randomly first. Apr16 comment Security of permutation cipher I don't understand that last part. How can we recover the plaintext if we know $\sigma_1$? Feb21 comment Get permutations from password Thank you for the answer. Would you elaborate a bit more? (I am not very familiar with cryptography.) Feb20 comment Get permutations from password @RickyDemer: No (even though I would be interested in knowing how this could be done as well). Dec22 comment What are the advantages of CBC over ECB? Arh... Ok, now I think I see it. I was thinking about the encryption as just being an XOR (or something else that commutes with XORing. In that case it wouldn't add anything, right?). Thanks for the answer. Dec22 comment What are the advantages of CBC over ECB? Can't you just generate the second picture from the third? (assuming you know the block size and IV) I am not still sure that I understand. Aug24 comment How do ciphers change plaintext into numeric digits for computing? @CodesInChaos: Thanks! I didn't know. I will research this and update my answer or delete the answer. Aug23 comment Can I make a cipher (ex: Vigenère) harder to break? @B-Con: Ahh, I see. So 2^(4.7) = 26. How would one actually do this? I am not sure that I understand. Aug23 comment Can I make a cipher (ex: Vigenère) harder to break? @CodesInChaos: Thanks for the comment. I don't want to use this for anything serious, I am just learning. I would like to understand how one might combine the Vigenere with something simple. Something that would be easy to understand and to implement. What do you mean by the 4.7 bit one? Aug20 comment Are there hash algorithms with variable length output? Thanks for the answer. Since you asked: The reason for my questions wasn't deep at all. I had thought about padding of keys/passwords, and was thinking that instead of padding key, one could just generate a hash of a specific length of a key. Thereby all key lengths should be "allowed", but I don't know if this is secure. I will probably ask a question about this later after I have thought more about it. Jun15 comment Assistance Cracking Classical Cipher Eli, I would have to agree with Hendrik. Of course one can find the key from your solution, but that doesn't help the OP learn how to actually find the key in future problems. Jun13 comment RSA Proof of Correctness Could you try to explain exactly what you do understand and what you don't understand? Do you understand Fermat's little theorem? What about the Chinese remainder theorem? Jun12 comment Looking for cipher that uses one ciphertext @Globalnomad: Ok, I understand now. It sounds like David's answer is what you need then. (I actually don't know enough about this...). Jun12 comment Looking for cipher that uses one ciphertext So just to make sure I understand. You want the teacher to just encrypt say one file, giving you one ciphertext. (so one plaintext and one ciphertext) And the you want to give the recipients each a different password, so that each password decrypts the message. But you want the result of the decryption to be different depending on who decrypted the message? So the teacher does not have different messages that he/she encrypts differently? Jun11 comment Hash function in PBKDF2 Thanks for the answer. Yes I am just doing this for fun. I don't actually need to encrypt anything. But I would like something that wasn't trivial and something that doesn't show obvious signs of pattern. I read more about the hash functions, and I see that I was wrong... Jun11 comment Looking for cipher that uses one ciphertext (I am also new to cryptography). Have you looked at RSA? Here the recipients have their one key that John can use to encrypt the message with. Thereby each will receive a message that "looks" different. Only the recipient will be able to decrypt the message. Jun10 comment Padding for the TEA Ok, so I think that I understand how to do the plaintext padding. If I want to use this PBKDF2, how exactly would I do that? I see that it requires salt. How, for example does one produce that? (This might be an entirely new question?)