# Tagged Questions

AES (Advanced Encryption Standard) is a symmetrical block-cipher algorithm with a 128-bit block size, and key sizes of 128, 192 or 256 bits.

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### AES-SIV security

I am invesigating the AES-SIV (rfc 5297) based block cipher. The construction of the S2V is lying on the AES-CMAC and dbl and XOR operation. Given a AAD the size of L and in the 128bit block ...
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### Derive a key from public data using a secret master key

Users in my system will be given a device that contains a 128-bit AES user key. The user key will be derived from 64 bits of public data related to the user, which is unique but very predictable (i.e. ...
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### Does the GCM authentication tag need to be protected?

I am just learning about the GCM mode of AES and I'd like to start using it in my software. However, I have a question about its use. As I understand it the output of a GCM encryption operation is ...
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### AES: keylength and password length? [closed]

What is the difference between the keylength and the length of a password for AES-256?
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### Is this an acceptable authenticated encryption?

After much deliberation, I've decided to use a normal Encrypt-then-MAC scheme instead of an authenticated encryption mode such as GCM as authenticated encryption primitive. This is due to the lack of ...
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### How difficult is it to find the “pre-image” of a block cipher?

Say that I have $$C_1 = AES_{k_1}(M_1)$$ How difficult would it be to find a key, K2 and plaintext M2 $$C_2 = AES_{k_2}(M_2)$$ such that $$C_1 == C_2$$ How would using a block cipher ...
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### Using same AES-GCM setup for multiple packets?

Most cryptographic libraries I've encountered uses some variant of processPlaintext(...) and then doFinal() to produce the ...
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### Review of AES encryption concept for an open source project

i'm working on an opensource project, A generator for static (html/js), password protected photo galleries. The generator AES 256 encrypts many images with the same key in PyCrypto, and decrypt them ...
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### What parts of AES encryption result are safe to pass on the network

I'm using AES to encrypt the message. both sender and receiver know the passphrase, but only sender knows IV and salt I assume that receiver also needs to know IV and salt to decypher text; is it ...
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### openssl logs showing keyblock length of only 88 bytes instead of 136 bytes

I was decrypting TLS encrypted data from wireshark using the openssl(TLS1.0 version) TLS logs which provides the complete key block which of size 136 bytes.Now i moved to TLS(1.2 version) in that Key ...
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### Partial decryption of large file in AES-GCM (or other modes)?

Lets assume a 4gig file that is internally made of 1 million pages of 4k bytes each (page). the file was originally AES-GCM encrypted these pages (or entire file) lives across the internet i.e. ...
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### Would a “Triple AES” (in the sense of how Triple Des works) serve for a dramatic increase in safety?

The system requires to be as paranoid as possible regarding security. One of the few contemplated changes to the current design is to use multiple encryption. First proposal was to use Serpent on top ...
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### Is this method for exchanging private key using RSA sound?

Bob know's Alice's public key, and he wants to make sure he's connecting to the one which has that key. Furthermore, Alice wants to verify when she gets a connection from Bob who'll give his public ...
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### is AES secure for java application licensing

I have to license a java application and want to code a quick implementation, the scheme I came up with is: 1) The Application calculates a string X which we assume to be the md5 sum of the computer'...
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### Deriving HMAC key and cipher key from passphrase? [duplicate]

I'm encrypting a file with AES-256 in CBC mode. I needed to add an HMAC for authentication and validation of the file contents and passphrase, so I used a SHA-256 HMAC over chunks of my file ...
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### Is storing original file size in an encrypted file header a bad idea?

I'm encrypting a file using AES-256 in CBC mode. I'm padding to the 16-byte input multiple by using the PKCS#7 limit. The problem I'm currently having is that if I'm transferring or reading the ...
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### Validating successful decryption in AES

I have a program which uses AES-256 in CBC mode to encrypt and decrypt files. As I have quickly realized, AES will even use an incorrect passphrase to decrypt data, which leaves me with no way to ...
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### AES key/ciphertext space sizes

This is giving me a brain ache now... If I have AES-128, block is 128 bit, then every plaintext (128-bit) can be encrypted to some ciphertext that is also 128-bit. This is the block size. But: 128-bit ...