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What happens if two messages are encrypted with the same key and nonce IV?
Encrypting the same block twice will result in the same ciphertext – leaking information to an adversary – and you can only encrypt 128 bit messages. An initialization vector (IV) or number-used-once (nonce) – I’ll use just IV – is used in most modes of operation to generate a ciphertext indistinguishable from random.
Why does IV need to be unique?
It depends… The key point is that if you ever reuse an IV, you open yourself up to cryptographic attacks that are easier to execute than those when you use a different IV every time. So, for every sequence where you need to start encrypting again, you need a new, unique IV.
Is AES-GCM block cipher?
AES-GCM is a block cipher mode of operation that provides high speed of authenticated encryption and data integrity.
What is the significance of initialization vector IV?
A continuously changing number used in combination with a secret key to encrypt data. Initialization vectors (IVs) are used to prevent a sequence of text that is identical to a previous sequence from producing the same exact ciphertext when encrypted.
Is GCM block cipher?
GCM is constructed from an approved symmetric key block cipher with a block size of 128 bits, such as the Advanced Encryption Standard (AES) algorithm that is specified in Federal Information Processing Standard (FIPS) Pub. 197 [2]. Thus, GCM is a mode of operation of the AES algorithm.
What’s the recommended IV size for AES GCM?
When using AES-GCM, a 96-bit IV is generally recommended. Most implementations I’ve seen also use 96-bit. However, I’m unsure on where this recommendation or convention comes from.
Why does Mac-AES-GCM recommend 12 bytes?
In the general case, the security goal is to reduce the probability that the internal 128-bit counter block ever takes the same value when instantiating the GCM cipher with a given key. That is catastrophic in combination with the CTR mode. The best strategy to minimize such probability depends on how the IV is generated.
Is there maximum number of invocations of GCM?
NIST SP-800 38D has a whole chapter – chapter 8 – dedicated discussing key and IV uniqueness and the maximum number of invocations of GCM. If the uniqueness of the IV / key combination cannot be met then security of GCM fails catastrophically.
Can a non 96 bit IV be used with GCM?
GCM being a stream cipher, it is totally malleable if the authentication mechanism fails (the MAC is the only thing preventing tampering). Moreover, there are mild concerns if you use a non-96-bit IV with NIST-spec GCM.