Which type of encryption is considered to be unbreakable if the stream is truly random and is as large as the plaintext and never reused in whole or…

The One-Time Pad (OTP) is an encryption technique that is theoretically proven to be unbreakable, a property known as perfect secrecy. This is achieved only when its strict implementation criteria are met: the key must be generated from a truly random source, it must be at least as long as the plaintext, and it must be used for only one message and then destroyed. When these conditions are fulfilled, the resulting ciphertext bears no statistical relationship to the plaintext, rendering any form of cryptanalysis futile without access to the key. The security of the OTP relies on the randomness and single-use nature of the key, not on computational difficulty.

B. One time Cryptopad (OTC): This is not a recognized term in the field of cryptography and serves as a distractor.

C. Cryptanalysis: This is the discipline of studying and breaking ciphers; it is the adversary's process, not a method of encryption.

D. Pretty Good Privacy (PGP): PGP is a robust hybrid encryption system, but its security is computational, not theoretical. It is considered breakable given sufficient computing power.

1. Shannon

C. E. (1949). Communication Theory of Secrecy Systems. Bell System Technical Journal

28(4)

656–715. In Section 14

"Perfect Systems

" Shannon formally defines and proves that a system like the one-time pad

where the key is random and as long as the message

achieves perfect secrecy. DOI: https://doi.org/10.1002/j.1538-7305.1949.tb00928.x

2. Katz

J.

& Lindell

Y. (2021). Introduction to Modern Cryptography (3rd ed.). CRC Press. In Chapter 2

"Perfectly Secret Encryption

" Definition 2.1 and the subsequent discussion on the one-time pad (Section 2.2) explicitly state that the cipher is perfectly secret if the key is chosen uniformly at random from the space of all possible keys of the same length as the message.

3. Boneh

D. (n.d.). CS255: Introduction to Cryptography

Lecture 2. Stanford University. The lecture notes for "Stream Ciphers and the One Time Pad" state

"The One Time Pad is a cipher that has a property called perfect secrecy... A cipher has perfect secrecy if P[ M=m | C=c ] = P[ M=m ] for all m in M

c in C." This is achieved when the key is random and used only once.