Otp

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One Time Pad Usage (OTP)SSG Ryan J. Gomez – U.S. Army

"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: NoneRisk Assessment: LowEnvironmental Considerations: None

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Evaluation

Evaluation: Show an understanding of OTP usage and productively participate in group discussion.

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Enabling Learning Objective (ELO)

ELO: Cryptology and History of OTP usage.

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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.➲ Encryption - The process of converting plaintext

into ciphertext.➲ 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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Overview of CryptographyWhat’s the point?

➲ Privacy - Would you be willing to send all of

your correspondence through the U.S. Mail

on the back of a postcard for all to read?

➲ Data Integrity - Provides assurance that a

message or file has not been altered

➲ Source Authentication - Provides a method

to identify the originator of a message or file

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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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Enabling Learning Objective

➲ ELO: Usage of OTPs in the Contemporary Operating Environment.

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Intelligence Information Securely

➲ *Intelligence Gathering

➲ *Itelligence Agent Reporting

➲ *Embedded Agent Reporting

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Enabling Learning Objective

➲ ELO: Understanding Cryptographic Systems

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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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Crypto Keys & AlgorithmsGeneral Concepts and Definitions

➲ As a password is used to access a computer system, a cryptographic key is a password or passphrase that is used to unlock an encrypted message.

➲ Different encryption systems offer different key lengths - Just as a longer password provides more security (WindowsNT excluded) the longer and more complex the key is, the more security an encryption system provides.

➲ A cryptographic algorithm is a mathematical function used for encryption and decryption. Most algorithms contain a certain number of “rounds.” This determines how many times the text will be run through the algorithm

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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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Check on Learning

➲ What is the most secure method of non-personal 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: Cypher and Decypher a One Time Pad message.

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Cyper and Decypher a OTP Message

➲ The one-time pad is a long sequence of random letters. These letters are combined with the plaintext message to produce the ciphertext. 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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Encipher OTP Message

➲ To encipher a message, you take the first letter in the plaintext 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 begining if the addition results in a number beyond 26 (Z).

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Decipher OTP Message

➲ To decipher a message, you take the first letter of the ciphertext and subtract the first random letter from the one-time pad. If the number is negative you wrap around to the end of the alphabet.

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Example

➲ Example➲ Plaintext: SECRETMESSAGE

➲ One-time pad: CIJTHUUHMLFRU

➲ Ciphertext: UMLKLNGLEDFXY➲ 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➲ 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 25

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Summary

➲ History

➲ Cryptography

➲ One Time Pad Usage