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  1. 1. 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
  2. 2. 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.
  3. 3. Safety, Risk, and Environmental Considerations Safety Requirements: None Risk Assessment: Low Environmental Considerations: None
  4. 4. Evaluation Evaluation: Correctly encrypt and decrypt a message using an OTP.
  5. 5. Enabling Learning Objective (ELO) ELO A: Cryptographic history and terminology.
  6. 6. 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.
  7. 7. 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>Plain Text (PT)- Data as message will be read - not encrypted. </li></ul><ul><li>Cipher Text (CT) - Data that has been encrypted and is ready for transmission. </li></ul>
  8. 8. Overview of Cryptography Terminology (Cont.) <ul><li>Encryption - The process of converting PT into CT. </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>
  9. 9. Enabling Learning Objective <ul><li>ELO B: Understanding and purpose of cryptographic systems </li></ul>
  10. 10. Information Security <ul><li>Threats: </li></ul><ul><li>Open Intelligence Gathering </li></ul><ul><ul><li>-Traditional & Social Media and Blogs </li></ul></ul><ul><li>Intelligence Agent </li></ul><ul><ul><li>-Actively attempts to gather sensitive information </li></ul></ul><ul><li>Embedded Agent </li></ul><ul><ul><li>-Trusted individual such as interpreters </li></ul></ul>
  11. 11. Information Security <ul><li>Countermeasures: </li></ul><ul><li>Operational Security (OPSEC) </li></ul><ul><li>Communications Security (COMSEC) Encryption </li></ul><ul><li>Protection of Data at Rest (DAR) </li></ul><ul><li>Physical Security (PHYSEC) </li></ul>
  12. 12. 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
  13. 13. 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 . . .
  14. 14. 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
  15. 15. 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.
  16. 16. Enabling Learning Objective <ul><li>ELO C: Usage of OTPs in the Contemporary Operating Environment (COE). </li></ul>
  17. 17. OTPs in the COE <ul><li>OTPs in conjunction with existing communications systems. </li></ul><ul><li>Strength of the OTP. </li></ul><ul><li>Weakness of the OTP. </li></ul>
  18. 18. Check on Learning <ul><li>What is the most secure method of non-personal (face to face) 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>
  19. 19. One Time Pad <ul><li>ELO D: Encrypt and decypher a OTP message. </li></ul>
  20. 20. Encrypt and Decrypt an OTP Message <ul><li>The one-time pad is a long sequence of random letters. These letters are combined with the PT message to produce the CT. </li></ul><ul><li>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. </li></ul><ul><li>This is the first and only encryption algorithm that has been proven to be unbreakable. </li></ul>
  21. 21. Encrypt an OTP Message <ul><li>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. </li></ul><ul><li>-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). </li></ul><ul><li>You add the two letters and subtract 1. </li></ul><ul><li>-When you add S and C and subtract 1, you get 21 which is U. </li></ul><ul><li>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). </li></ul>
  22. 22. Decrypt an OTP Message <ul><li>To decrypt a message, you take the first letter of the CT and subtract the first random letter from the OTP and add 1. </li></ul><ul><li>If the number is negative you wrap around to the end of the alphabet. </li></ul>
  23. 23. 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 26 </li></ul><ul><li>Encrypt: Plain Text (PT) Character + Cipher Text (CT) Character – 1 = Encrypted Letter (If more than 26, subtract 26) </li></ul><ul><li>Decrypt: Encrypted Letter – CT Character + 1 = PT Letter (if result is negative add 26) </li></ul>
  24. 24. Demonstration <ul><li>Encrypt: Plain Text (PT) Character + Cipher Text (CT) Character – 1 = Encrypted Letter (If more than 26, subtract 26) </li></ul><ul><li>Decrypt: Encrypted Letter – CT Character + 1 = PT Letter (if result is negative add 26) </li></ul>Today's OTP: PQYQ FWYC XQVV EYPL GJNS WCQI PPXR LQVZ AZSN ZEVL AJWA XHUN GUWU EOTC RMGP WSRE Today's Messages Encrypt: PAININBRAIN Decrypt: LYLD NJEN LB 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
  25. 25. Summary <ul><li>History </li></ul><ul><li>Cryptography </li></ul><ul><li>One Time Pad Usage </li></ul>