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Code versus Ciphers

Updated Jan 30, 2024 ·

Code​

A system that substitutes one word or phrase for another. Codes are intended to provide secrecy and/or efficiency. An example of a code is the "Ten" code which is used by the police and other organizations who communicate by radio

The Ten-Code, also known as ten signals, is a set of code words used to represent common phrases in voice communication, particularly in law enforcement and emergency services. These codes help simplify and standardize radio communications, making them more efficient and reducing misunderstandings.

Here are some examples:

  • 10-1: Signal Weak
  • 10-2: Signal Good
  • 10-3: Stop Transmitting
  • 10-4: Acknowledgment (OK)
  • 10-5: Relay
  • 10-6: Busy
  • 10-7: Out of Service
  • 10-8: In Service
  • 10-9: Repeat
  • 10-10: Fight in Progress

Ciphers​

A cipher is an algorithm used to encrypt and decrypt information, transforming plain text into coded (cipher) text and vice versa.

  • Ciphers ensure data confidentiality
  • Central to encryption protocols.

Types of Ciphers:

  • Stream Cipher
  • Block Cipher

Stream Ciphers​

Stream Ciphers encrypt data bit by bit or byte by byte in a continuous stream.

  • Performs encryption on single byte at a time.
  • Uses a key stream generator to create a pseudo-random sequence of bits (the key stream).
  • The key stream is then XORed with the plaintext to produce ciphertext.

Common Features:

  • Uses same key for encryption and decryption.
  • Implemented mostly on hardware-based solutions.
  • Often used in real-time applications where data is continuously transmitted (e.g., streaming services).
  • Vulnerable to certain types of attacks if key stream is reused or not sufficiently random.

Examples:

  • RC4
  • Salsa20
  • ChaCha20

Block Ciphers​

Block Ciphers break the input into fixed-size blocks (e.g., 64-bit or 128-bit) and performs the encryption on each block.

  • Performs encryption on per block basis.
  • A block of plaintext is processed with a key to produce a block of ciphertext.
  • Multiple rounds of transformation can also be used (e.g., substitution and permutation).

Common Features:

  • Easier to implement, less susceptible to security problems.
  • Implemented mostly on software solutions.
  • Often used in protocols and file encryption, where data is processed in chunks.
  • Require padding when the plaintext doesn't evenly divide into block sizes.
  • Can be operated in various modes to enhance security or support specific applications.

Examples:

  • AES
  • DES
  • 3DES

Building Blocks of Modern Cryptography​

Encryption and decryption are fundamental processes in securing data. They transform readable data into an unreadable format and vice versa, ensuring that sensitive information remains confidential during transmission and storage. Two primary methods used in these processes are substitution ciphers and transposition ciphers.

Substitution Cipher​

A substitution cipher replaces elements of the plaintext with corresponding elements of the ciphertext based on a predetermined system.

  • Each letter or group of letters in the plaintext is replaced with another letter or group of letters.
  • The Caesar cipher is a well-known substitution cipher where each letter in the plaintext is shifted a certain number of places down the alphabet.
  • Substitution ciphers can be simple monoalphabetic ciphers or more complex polyalphabetic ciphers, which use multiple substitution alphabets.

Transposition Cipher​

A transposition cipher rearranges the characters of the plaintext according to a specific system to produce the ciphertext.

  • The order of the characters is changed, but the characters themselves remain the same.
  • One common type is the rail fence cipher, where the plaintext is written in a zigzag pattern across multiple "rails" and then read row by row.
  • Another example is the columnar transposition cipher, which arranges the plaintext into columns and then permutes the columns according to a key.

Common Ciphers​

Cease Cipher​

Named after Julius Caesar, it is a simple substitution cipher where each letter in the plaintext is shifted a certain number of positions down or up the alphabet.

  • Shifts each letter in the plaintext a certain number of positions along the alphabet.
  • The number of positions to shift, typically between 1 and 25.
  • Example: With a shift of 3, 'A' becomes 'D', 'B' becomes 'E', and so on.
  • ROT2 - two shifts in positions
  • ROT3 - three shifts in positions, and so on.

Although it's historically significant, the Caesar Cipher is not used for serious encryption today due to its simplicity and vulnerability to straightforward cryptanalysis

Vigenere Cipher​

The Vigenère Cipher is a type of polyalphabetic substitution cipher that uses a repeating key phrase to determine shifting patterns for each letter in the plaintext, offering greater security than simple substitution ciphers.

  • A key phrase, repeated to match the plaintext length, determines the shift for each letter.
  • To decrypt, use the same key to reverse the shifts and recover the plaintext.

Strengths:

  • Provides increased complexity, making frequency analysis and brute-force attacks more difficult.

Weaknesses:

  • Susceptible to Kasiski examination and Friedman tests, which can reveal key patterns and lengths, leading to cryptanalysis.

Example:

  • With the key "LEMON," the plaintext "HELLO" is encrypted by shifting each letter according to the corresponding letter in the key, resulting in "OIWWC."

Exlusive OR (XOR)​

Exclusive OR (XOR) is a binary operation used extensively in cybersecurity and cryptography. It operates on bits, returning 1 if the bits are different and 0 if they are the same. Here's a concise description with key bullet points:

  • XOR compares two bits; if they're different, it outputs 1; if they're the same, it outputs 0.
  • XOR is reversible, allowing data encrypted with a key to be decrypted by XORing again with the same key.

Applications:

  • Encryption:

    • Commonly used in stream ciphers and some block ciphers to combine plaintext with a key stream, creating ciphertext.

  • One-Time Pad (OTP):

    • A theoretically unbreakable encryption method that uses XOR with a key as long as the plaintext, provided the key is truly random and never reused.

  • Data Manipulation:

    • XOR can be used to toggle bits or swap values without additional storage.

  • Error Detection/Correction:

    • In parity checks and error-correcting codes, XOR helps identify errors in transmitted or stored data.

Security Considerations:

  • Key Management:

    • Security in XOR-based encryption relies heavily on key secrecy and randomness.

  • Vulnerabilities:

    • If the key is reused or predictable, XOR-based encryption is susceptible to various attacks, including known-plaintext attacks.