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
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.
Evaluation Evaluation: Show an understanding of OTP usage and productively participate in group discussion.
Enabling Learning Objective (ELO) ELO: Cryptology and History of OTP usage.
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.
Overview of Cryptography Terminology <ul><li>Cryptographic/Cipher System - A method of disguising a message so only authorized users may read it. </li></ul><ul><li>Cryptology - The study of cryptography. </li></ul><ul><li>Encryption - The process of converting plaintext into ciphertext. </li></ul><ul><li>Decryption - The process of converting ciphertext back to its original plaintext. </li></ul><ul><li>Cryptographic Algorithm - The computational procedure used to encrypt and decrypt messages. </li></ul><ul><li>Cryptanalysis - The process of finding a weakness in, or actual breaking of, a cryptographic system. </li></ul>
Overview of Cryptography What’s the point? <ul><li>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? </li></ul><ul><li>Data Integrity - Provides assurance that a message or file has not been altered </li></ul><ul><li>Source Authentication - Provides a method to identify the originator of a message or file </li></ul>
Types of Cryptographic Systems Secret Codes <ul><li>The simplest and oldest way to send a secret message to someone. The code must be known to the sender or recipient. </li></ul>Code Phrase True Meaning My coffee is cold Pass the cream Launch the missiles Don’t launch the missiles
Enabling Learning Objective <ul><li>ELO: Usage of OTPs in the Contemporary Operating Environment. </li></ul>
Enabling Learning Objective <ul><li>ELO: Understanding Cryptographic Systems </li></ul>
Types of Cryptographic Systems Ciphers <ul><li>Substitution ciphers are the simplest type of cipher system. </li></ul><ul><li>Each letter of the alphabet is assigned to a number or different letter. </li></ul><ul><li>ROT13 is a commonly used cipher. </li></ul>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 . . .
Types of Cryptographic Systems One-Time Pads <ul><li>One-Time Pads uses a different key for a specific time period. </li></ul><ul><li>Truly secure, no patterns evolve. </li></ul><ul><li>Most vulnerabilities due to human carelessness. </li></ul>Decrypted Text 14 07 09 06 10 02 25 13 17 08 15 One-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
Crypto Keys & Algorithms General Concepts and Definitions <ul><li>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. </li></ul><ul><li>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. </li></ul><ul><li>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 </li></ul>
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.
Check on Learning <ul><li>What is the most secure method of non-personal communication? </li></ul><ul><li>What method of encryption was utilized during WWII? </li></ul><ul><li>What is the most secure method of generating a key? </li></ul>
One Time Pad <ul><li>ELO: Cypher and Decypher a One Time Pad message. </li></ul>
Cyper and Decypher a OTP Message <ul><li>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. </li></ul>
Encipher OTP Message <ul><li>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). </li></ul>
Decipher OTP Message <ul><li>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. </li></ul>
Example <ul><li>Example </li></ul><ul><li>Plaintext: SECRETMESSAGE </li></ul><ul><li>One-time pad: CIJTHUUHMLFRU </li></ul><ul><li>Ciphertext: UMLKLNGLEDFXY </li></ul><ul><li>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 </li></ul><ul><li>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 </li></ul>
Summary <ul><li>History </li></ul><ul><li>Cryptography </li></ul><ul><li>One Time Pad Usage </li></ul>
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