Unit 4 – Introduction to Cryptography

A comprehensive set of vocabulary flashcards covering key terms, algorithms, objectives, and applications introduced in the Unit 4 lecture on Cryptography.

Cryptology

The broad study of secure communication, encompassing cryptography (creating ciphers) and cryptanalysis (breaking them).

Cryptography

The art and science of protecting information by converting plaintext into ciphertext and vice versa; focused on encryption methods.

Cryptanalysis

The study of cryptographic systems to discover weaknesses or recover information, i.e., the art of breaking ciphers.

Confidentiality

Cryptographic objective that ensures only intended recipients can read the message.

Integrity

Assurance that data has not been altered during storage or transmission.

Authentication

Verification of the identity of a sender or device.

Non-repudiation

Proof that a sender actually sent a message, preventing denial of involvement.

Plaintext

Readable data ready for encryption by a cipher.

Cleartext

Unencrypted, human-readable data; may be encoded but not encrypted.

Cipher

Algorithm that converts plaintext into ciphertext using a key.

Key

Secret value that governs transformation rules in a cipher; longer keys usually give stronger security.

Encryption

Process of disguising plaintext as ciphertext using a cipher and key.

Decryption

Process of reverting ciphertext back to plaintext with the appropriate key.

Adversary

Any unauthorized or malicious entity attempting to compromise a cryptographic system.

Substitution Cipher

Cipher that replaces each element of plaintext with another element (e.g., Caesar, Playfair).

Transposition Cipher

Cipher that rearranges the order of plaintext characters (e.g., Rail Fence).

Scytale Cipher

Ancient Spartan transposition cipher using a parchment strip wrapped around a rod.

Kamasutra Cipher

4th-century BCE Indian substitution cipher described in the Kamasutra for private messages.

Caesar Cipher

Classical substitution cipher shifting letters by a fixed number, famously by 3.

Playfair Cipher

5×5 grid substitution cipher encrypting text in letter pairs (bigrams).

Rail Fence Cipher

Transposition cipher writing text in a zigzag pattern across rails and reading row-by-row.

Symmetric Encryption

Encryption that uses the same secret key for both encryption and decryption.

Asymmetric Encryption

Encryption that uses a public key for encryption and a separate private key for decryption (or vice versa).

Steganography

Technique of hiding a secret message inside another file (image, audio, video) so its presence is concealed.

Hash Function

One-way algorithm that converts data into a fixed-length hash (message digest).

Block Cipher

Symmetric cipher that encrypts fixed-size blocks of data (64 or 128 bits).

Stream Cipher

Symmetric cipher that encrypts data one byte or bit at a time for continuous streams.

Data Encryption Standard (DES)

Legacy 56-bit key block cipher; considered insecure today.

Triple DES (3DES)

Applies DES three times for more security; officially retired in 2023.

Advanced Encryption Standard (AES)

Widely used block cipher with 128-bit blocks and key sizes of 128/192/256 bits.

SEAL

Software-Optimized Encryption Algorithm; fast 160-bit-key stream cipher alternative to AES.

RC4

Rivest stream cipher once common for web traffic; now considered insecure.

Diffie-Hellman (DH)

Asymmetric algorithm enabling two parties to agree on a shared secret over an insecure channel.

Elliptic Curve Cryptography (ECC)

Family of asymmetric techniques using elliptic curves, providing strong security with shorter keys.

ElGamal

Asymmetric encryption scheme based on DH; produces ciphertext about twice the size of plaintext.

Digital Signature Algorithm (DSA)

Algorithm specified by DSS for creating digital signatures; based on ElGamal.

RSA

Widely used public-key algorithm relying on the difficulty of factoring large integers.

Embedded Data (Steganography)

The actual secret message hidden inside a cover file.

Cover File

Normal-looking carrier (image/audio/video) used to hide embedded data in steganography.

Stego File

Final file containing the hidden data after steganographic embedding.

Stego Key

Secret that controls how data is embedded or extracted in steganography.

Message Digest

Fixed-length output (hash value) produced by a hash function; digital fingerprint of data.

MD5

128-bit hash function by Ron Rivest; fast but vulnerable to collisions, legacy only.

SHA-1

160-bit hash from NSA (1995); collision-prone and no longer recommended for security use.

SHA-2

Family including SHA-224/256/384/512; currently trusted and widely deployed.

SHA-3

Next-generation hash family (Keccak) introduced by NIST in 2012, resistant to known attacks.

Keccak

Underlying sponge construction algorithm used in SHA-3.

Salting

Adding a random value to each password before hashing to defeat rainbow table attacks.

Rainbow Table Attack

Precomputed table of hash values used to reverse weakly protected hashes; mitigated by salting.

Digital Signature

Cryptographic technique that binds a signer to data by hashing it and encrypting the hash with the signer’s private key.

Digital Certificate

X.509 file that binds a public key to an entity’s identity, signed by a Certificate Authority.

Certificate Authority (CA)

Trusted organization that issues, signs, and manages digital certificates.

Pretty Good Privacy (PGP)

Hybrid cryptosystem combining symmetric encryption (for data) with asymmetric encryption (for key exchange and authentication).