One-time pad

one-time tapeone time padone-time padsmake this scheme secureone time padsone-time cipher padsone-time-padone-time-pad encryption
In cryptography, the one-time pad (OTP) is an encryption technique that cannot be cracked, but requires the use of a one-time pre-shared key the same size as, or longer than, the message being sent.wikipedia
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Cryptography

cryptographiccryptographercryptology
In cryptography, the one-time pad (OTP) is an encryption technique that cannot be cracked, but requires the use of a one-time pre-shared key the same size as, or longer than, the message being sent.
There exist information-theoretically secure schemes that cannot be broken even with unlimited computing power—an example is the one-time pad—but these schemes are more difficult to implement than the best theoretically breakable but computationally secure mechanisms.

Joseph Mauborgne

Joseph O. Mauborgne
One-time use came later, when Joseph Mauborgne recognized that if the key tape were totally random, then cryptanalysis would be impossible.
Joseph Oswald Mauborgne (February 26, 1881 – June 7, 1971) co-invented the one-time pad with Gilbert Vernam of Bell Labs.

Gilbert Vernam

VernamVernam cipherGilbert S. Vernam
On July 22, 1919, U.S. Patent 1,310,719 was issued to Gilbert S. Vernam for the XOR operation used for the encryption of a one-time pad.
Gilbert Sandford Vernam (3 April 1890 – 7 February 1960) was a Worcester Polytechnic Institute 1914 graduate and AT&T Bell Labs engineer who, in 1917, invented an additive polyalphabetic stream cipher and later co-invented an automated one-time pad cipher.

Cryptographically secure pseudorandom number generator

cryptographically secure pseudo-random number generatorcryptographic pseudorandom number generatorcryptographically secure
There is some ambiguity to the term "Vernam cipher" because some sources use "Vernam cipher" and "one-time pad" synonymously, while others refer to any additive stream cipher as a "Vernam cipher", including those based on a cryptographically secure pseudorandom number generator (CSPRNG).
And in the case of one-time pads, the information-theoretic guarantee of perfect secrecy only holds if the key material comes from a true random source with high entropy, and thus any kind of pseudo-random number generator is insufficient.

Ciphertext

ciphertextscipher textciphered text
If the key is (1) truly random, (2) at least as long as the plaintext, (3) never reused in whole or in part, and (4) kept completely secret, then the resulting ciphertext will be impossible to decrypt or break.
Substitution cipher: the units of plaintext are replaced with ciphertext (e.g., Caesar cipher and one-time pad)

Stream cipher

stream cypherstream ciphersstream
There is some ambiguity to the term "Vernam cipher" because some sources use "Vernam cipher" and "one-time pad" synonymously, while others refer to any additive stream cipher as a "Vernam cipher", including those based on a cryptographically secure pseudorandom number generator (CSPRNG).
Stream ciphers can be viewed as approximating the action of a proven unbreakable cipher, the one-time pad (OTP), sometimes known as the Vernam cipher.

Key (cryptography)

keykeysencryption key
In this technique, a plaintext is paired with a random secret key (also referred to as a one-time pad). Then, each bit or character of the plaintext is encrypted by combining it with the corresponding bit or character from the pad using modular addition.
For the one-time pad system the key must be at least as long as the message.

Frank Miller (cryptographer)

Frank Miller
First described by Frank Miller in 1882, the one-time pad was re-invented in 1917.
He invented the one-time pad in 1882, 35 years before the patent issued to Gilbert Vernam.

Multiple encryption

cascadedsuperenciphermentsuperencryption
For added security, secret numbers could be combined with (usually modular addition) each code group before transmission, with the secret numbers being changed periodically (this was called superencryption).
With the exception of the one-time pad, no cipher has been theoretically proven to be unbreakable.

Claude Shannon

ShannonClaude E. ShannonC.E. Shannon
The final discovery was made by information theorist Claude Shannon in the 1940s who recognized and proved the theoretical significance of the one-time pad system.
While he was at Bell Labs, Shannon proved that the cryptographic one-time pad is unbreakable in his classified research that was later published in October 1949.

Pad

The "pad" part of the name comes from early implementations where the key material was distributed as a pad of paper, so that the top sheet could be easily torn off and destroyed after use.
One-time pad, a method of cryptography

Cipher

cipherscyphercipher machine
Diplomats had long used codes and ciphers for confidentiality and to minimize telegraph costs.
It is possible to create a secure pen and paper cipher based on a one-time pad though, but the usual disadvantages of one-time pads apply.

Leo Marks

Marks, Leoswitch
Leo Marks describes inventing such a system for the British Special Operations Executive during World War II, though he suspected at the time that it was already known in the highly compartmentalized world of cryptography, as for instance at Bletchley Park.
He was credited with inventing the letter one-time pad, but while he did independently discover the method, he later found it already in use at Bletchley.

Quantum key distribution

quantum encryptionQKDDifferential phase-shift quantum key distribution
Quantum key distribution also proposes a solution to this problem, assuming fault-tolerant quantum computers.
The algorithm most commonly associated with QKD is the one-time pad, as it is provably secure when used with a secret, random key.

Vladimir Kotelnikov

Vladimir A. KotelnikovVladimir Aleksandrovich Kotelnikov
At the same time, Soviet information theorist Vladimir Kotelnikov had independently proved absolute security of the one-time pad; his results were delivered in 1941 in a report that apparently remains classified.
Kotelnikov was also involved in cryptography, proving the absolute security of the one-time pad; his results were delivered in 1941, the time of Nazi Germany's invasion of the Soviet Union, in a report that apparently remains classified.

Nitrocellulose

nitrate filmguncottoncellulose nitrate
To increase security, one-time pads were sometimes printed onto sheets of highly flammable nitrocellulose, so that they could be quickly burned after use.
As a medium for cryptographic one-time pads, they make the disposal of the pad complete, secure, and efficient.

Venona project

Venonabrokencryptanalysts
The most famous exploit of this vulnerability occurred with the Venona project.
This message traffic, which was encrypted with a one-time pad system, was stored and analyzed in relative secrecy by hundreds of cryptanalysts over a 40-year period starting in the early 1940s.

Entropy (information theory)

entropyinformation entropyShannon entropy
Mathematically, this is expressed as, where \Eta(M) is the information entropy of the plaintext and \Eta(M|C) is the conditional entropy of the plaintext given the ciphertext C.
For example, a 1,000,000-digit binary one-time pad using exclusive or. If the pad has 1,000,000 bits of entropy, it is perfect.

Information theory

information theoristinformation-theoreticinformation
Claude Shannon proved, using information theory considerations, that the one-time pad has a property he termed perfect secrecy; that is, the ciphertext C gives absolutely no additional information about the plaintext.
Information theoretic security refers to methods such as the one-time pad that are not vulnerable to such brute force attacks.

Rockex

A few British one-time tape cipher machines include the Rockex and Noreen.
Rockex, or Telekrypton, was an offline one-time tape cipher machine known to have been used by Britain and Canada from 1943.

Exclusive or

XORexclusive-orexclusive disjunction
On July 22, 1919, U.S. Patent 1,310,719 was issued to Gilbert S. Vernam for the XOR operation used for the encryption of a one-time pad.
Exclusive-or is sometimes used as a simple mixing function in cryptography, for example, with one-time pad or Feistel network systems.

Substitution cipher

substitutionmonoalphabetic substitution ciphersubstitution ciphers
Conventional symmetric encryption algorithms use complex patterns of substitution and transpositions.
One type of substitution cipher, the one-time pad, is quite special.

Noreen

A few British one-time tape cipher machines include the Rockex and Noreen.
Noreen, or BID 590, was an off-line one-time tape cipher machine of British origin.

SIGSALY

Green Horneta special scramblercomputers of the era
The World War II voice scrambler SIGSALY was also a form of one-time system.
The insecurity of most telephone scrambler schemes led to the development of a more secure scrambler, based on the one-time pad principle.

Secure communication

secureinterceptedsecure global communication
Starting in 1988, the African National Congress (ANC) used disk-based one-time pads as part of a secure communication system between ANC leaders outside South Africa and in-country operatives as part of Operation Vula, a successful effort to build a resistance network inside South Africa.
To maintain secrecy, the Green Hornet was kept in a closet labeled It is said that because the Green Hornet works by a one-time pad it cannot be beaten.