What is potential problem with using the same Key and Nonce (IV) values in two different encryption operations of a stream cipher?
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Using the same Key and Nonce (IV) values in two different encryption operations of a stream cipher can lead to a serious security vulnerability known as a "two-time pad" problem.
The two-time pad problem occurs when the same Key and Nonce values are used to encrypt two different plaintexts. In stream ciphers, the Key and Nonce are combined to generate a stream of random bits, which are then XORed with the plaintext to produce the ciphertext.
If the Key and Nonce are reused, the same stream of random bits will be generated. This means that when the stream is XORed with one plaintext to produce the ciphertext, and then XORed with another plaintext to produce a second ciphertext, an attacker can perform a bitwise XOR operation of the two ciphertexts to obtain the XOR of the two plaintexts.
This allows the attacker to gain knowledge about the original plaintexts without knowing the actual Key or Nonce values. By analyzing patterns, statistical properties, or other known information about the plaintexts, the attacker may be able to infer the content of the original messages.
To avoid this vulnerability, it is crucial to use unique Key and Nonce values for each encryption operation in a stream cipher. This ensures that the generated stream of random bits is different for each encryption, preventing the attacker from exploiting the two-time pad problem.
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