Otp2

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One Time Pad (OTP) Usage

SSG Ryan J. Gomez – U.S. Army

Army Basic Instructors Course

"If you think cryptography can solve your problem, then you don't understand your problem and you don't understand cryptography." -- Bruce Schneier

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Terminal Learning Objective

Terminal Learning Objective:

Action: Correctly identify and utilize a OTP.

Condition: Given a OTP, correct keying material, and scratch paper & writing utensil in a classroom environment.

Standard: Decrypt and Encrypt a OTP message.

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Safety, Risk, and Environmental Considerations

Safety Requirements: None

Risk Assessment: Low

Environmental Considerations: None

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Evaluation

Evaluation: Correctly encrypt and decrypt a message using an OTP.

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Enabling Learning Objective (ELO)

ELO A: Cryptographic history and terminology.

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History of Cryptography and OTP Usage

* The earliest methods of cryptography were altered hieroglyphics attempting to pass secret messages.

* WWII messages were primarily mechanically generated.

* Modern cryptography utilizes mathematically based encryption.

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Overview of Cryptography Terminology

Cryptographic/Cipher System - A method of disguising a message so only authorized users may read it.

Cryptology - The study of cryptography.

Plain Text (PT)- Data as message will be read - not encrypted.

Cipher Text (CT) - Data that has been encrypted and is ready for transmission.

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Overview of Cryptography Terminology (Cont.)

Encryption - The process of converting PT into CT.

Decryption - The process of converting ciphertext back to its original plaintext.

Cryptographic Algorithm - The computational procedure used to encrypt and decrypt messages.

Cryptanalysis - The process of finding a weakness in, or actual breaking of, a cryptographic system.

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Enabling Learning Objective

➲ ELO B: Understanding and purpose of cryptographic systems

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Information Security

Threats:

Open Intelligence Gathering-Traditional & Social Media and Blogs

Intelligence Agent -Actively attempts to gather sensitive

information

Embedded Agent -Trusted individual such as interpreters

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Information Security

Countermeasures:

Operational Security (OPSEC)

Communications Security (COMSEC) Encryption

Protection of Data at Rest (DAR)

Physical Security (PHYSEC)

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Types of Cryptographic SystemsSecret Codes

The simplest and oldest way to send a secret message to someone. The code must be known to the sender or recipient.

Code Phrase True Meaning

My coffee is cold

Pass the cream

Launch the missiles

Don’t launch the missiles

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Types of Cryptographic Systems

Ciphers➲ Substitution ciphers are the simplest type of cipher

system.➲ Each letter of the alphabet is assigned to a number

or different letter.➲ ROT13 is a commonly used cipher.

A B C D E F G H I J K L M

1 2 3 4 5 6 7 8 9 A B C . . .

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Types of Cryptographic SystemsOne-Time Pads

➲ One-Time Pads uses a different key for a specific time period.

➲ Truly secure, no patterns evolve.➲ Most vulnerabilities due to human carelessness.

14 07 09 06 10 02 25 13 17 08 15One-Time Pad - Shift each encrypted letter x places to the right

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

fazmyqbgnke

Encrypted Message

This is a test

Decrypted Text

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One Time Pad

The above is an example of a page from a standard one time pad. The encryption & decryption keys are impossible to decipher when generated using entirely random keys.

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Enabling Learning Objective

ELO C: Usage of OTPs in the Contemporary Operating Environment (COE).

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OTPs in the COE

OTPs in conjunction with existing communications systems.

Strength of the OTP.

Weakness of the OTP.

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Check on Learning

➲ What is the most secure method of non-personal (face to face) communication?

➲ What method of encryption was utilized during WWII?

➲ What is the most secure method of generating a key?

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One Time Pad

ELO D: Encrypt and decypher a OTP message.

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Encrypt and Decrypt an OTP Message

The one-time pad is a long sequence of random letters. These letters are combined with the PT message to produce the CT.

To decipher the message, a person must have a copy of the one-time pad to reverse the process. A one-time pad should be used only once (hence the name) and then destroyed.

This is the first and only encryption algorithm that has been proven to be unbreakable.

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Encrypt an OTP Message

To encrypt a message, you take the first letter in the PT message and add it to the first random letter from the one-time pad.

-For example, suppose you are enciphering the letter S (the 19th letter of the alphabet) and the one-time pad gives you C (3rd letter of the alphabet).

You add the two letters and subtract 1. -When you add S and C and subtract 1, you get 21 which is U.

Each letter is enciphered in this method, with the alphabet wrapping around to the beginning if the addition results in a number beyond 26 (Z).

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Decrypt an OTP Message

To decrypt a message, you take the first letter of the CT and subtract the first random letter from the OTP and add 1.

If the number is negative you wrap around to the end of the alphabet.

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Example

ExamplePlaintext: SECRETMESSAGE

One-time pad: CIJTHUUHMLFRU

Ciphertext: UMLKLNGLEDFXYA B C D E F G H I J K L M N O P Q R S T U V W X Y Z1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

Encrypt: Plain Text (PT) Character + Cipher Text (CT) Character – 1 = Encrypted Letter (If more than 26, subtract 26)

Decrypt: Encrypted Letter – CT Character + 1 = PT Letter (if result is negative add 26)

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Demonstration

Encrypt: Plain Text (PT) Character + Cipher Text (CT) Character – 1 = Encrypted Letter (If more than 26, subtract 26)

Decrypt: Encrypted Letter – CT Character + 1 = PT Letter (if result is negative add 26)

A B C D E F G H I

1 2 3 4 5 6 7 8 9

J K L M N O P Q R

10 11 12 13 14 15 16 17 18

S T U V W X Y Z

19 20 21 22 23 24 25 26

Today's OTP:PQYQ FWYC XQVV EYPLGJNS WCQI PPXR LQVZAZSN ZEVL AJWA XHUNGUWU EOTC RMGP WSRE

Today's MessagesEncrypt:PAININBRAINDecrypt:LYLD NJEN LB

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Summary

➲ History

➲ Cryptography

➲ One Time Pad Usage