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4
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1answer
75 views

Do IVs need to be unpredictable?

I am encrypting a sequence of messages with AES/CTR. For each sequence, I generate a random initial IV, say IV(0). Define IV(i) = MD5(IV(i - 1)) for i = 1, ..., n. Then for each message m(i), I ...
2
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0answers
56 views

For use with RC4 how do I combine a reused key and an initialization vector

I am an a-level student writing an encryption program using an rc4 implementation I have written myself. I have the basic algorithm coded correctly (and I have checked that some ciphertext for a given ...
0
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0answers
74 views

Cryptographic Testing

Given an algorithm (say, AES), how to create/generate test vectors? I have tried using the NIST test vectors for AES and found it to be working fine with a package of "chilkat". Suppose, for a ...
5
votes
2answers
779 views

Can the IV + Salt be the same?

During my encryption app i've got the password creation bit: PBEKeySpec spec = new PBEKeySpec(password.toCharArray(), salt, 10000, keyLength); and later on the actual encryption part: ...
0
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0answers
63 views

Possible CPA or CCA attack when using AES-CBC mode under the following situation?

Both client and server know a shared key in advance. Both sides us EVP_BytesToKey() derive a pair of same key and same IV. Then, client and server start transferring data encrypted by AES-CBC mode ...
1
vote
2answers
453 views

What's the point of the nonce in CTR mode?

Does having a nonce in CTR mode actually improve security (vs. just using 1, 2, 3, etc. - basically a constant nonce of 0)? As far as I can tell, the best-case scenario security-wise is that the ...
1
vote
3answers
2k views

Is Salt, IV and Key necessary when encrypting password in a database using AES? If so, how should they be used?

Imagine I have a website with user accounts. I want to authenticate users, so I need to know if the password they provide matches the one stored in my database. To protect the passwords from prying ...
1
vote
1answer
121 views

How to generate Initalization Vectors correctly

I'm working on a project that splits large files into several encrypted fixed-size blocks (e.g. 4KiB). Those blocks shall be used to be stored persistently on a storage device. Blocks are encrypted ...
3
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2answers
3k views

Why would you need a salt for AES-CBS when IV is already randomly generated and stored with the encrypted data?

I was looking at this code and came across these comments which says encrypting without a salt is insecure. Why would it be insecure when you are already using a random IV for each value? I think the ...
0
votes
1answer
314 views

encrypting a file with an RSA key

I wrote a java program to encrypt and decrypt files using AES algorithm in CBC mode and a random initialization vector. but there is something fundamental I'm not understanding:first I generate a ...
3
votes
3answers
395 views

Is there an attack that can modify ciphertext while still allowing it to be decrypted?

Is there any way an encrypted file using AES-256 could be modified without alerting the file owner, ie., so it can still be decrypted with the same key? I know that without an initialization vector ...
4
votes
2answers
6k views

Using AesCryptoServiceProvider in C#, should using an incorrect IV mangle just the first block?

This question was also asked on StackOverflow, but with no answers, and I thought this may be a better exchange, since I have the same question. ...
6
votes
2answers
1k views

Should AES always give the same output?

I'm having trouble understanding AES and would like to know if encrypting the same text with the same key two times in a row should give the same output. Is there any salt or something that would ...
5
votes
3answers
505 views

How do poor-quality initialization vectors affect the security of CBC mode?

(If the consensus is that this question belongs on crypto, rather than here, please feel free to [tell me to] migrate it.) From what I have read (looking specifically at AES in Cipher Block Chaining ...
2
votes
1answer
93 views

Is it safe to derive an IV partially from the secret data if it is hashed before use?

To help ensure uniqueness of IV's used in a CFB AES-256 cipher, software I know of gathers bits from various sources including the plaintext being enciphered, and runs that through an SHA-256 hash. ...