Glossary of Terms
AES (Advanced Encryption Standard)
AES is a symmetric-key block cipher standardized by NIST in 2001, designed by Vincent Rijmen and Joan Daemen.
It operates on 128-bit blocks with keys of 128, 192, or 256 bits, and is based on a Substitution–Permutation Network.
AES is fast, secure, and widely implemented in both software and hardware (including CPU instructions).
It remains the global standard for symmetric encryption, used in TLS, SSH, disk encryption, and countless applications.
ECB (Electronic Code Book)
ECB is the simplest block cipher mode of operation: it encrypts each block independently with the same key.
While easy to implement, it is insecure because identical plaintext blocks produce identical ciphertext blocks.
This leaks patterns in the input (e.g., images encrypted with ECB visibly preserve outlines).
Because of this, ECB is almost never used in practice and is considered unsafe.
RSA (Rivest–Shamir–Adleman)
RSA is one of the first public-key cryptosystems, invented in 1977 by Ron Rivest, Adi Shamir, and Leonard Adleman.
It allows secure key exchange, encryption, and digital signatures by relying on the mathematical difficulty of factoring large integers.
RSA keys are typically 2048 or 3072 bits today. While still widely used, modern protocols increasingly migrate to elliptic-curve cryptography (ECC) for better performance and smaller key sizes.
Padding in RSA
RSA encryption without padding is deterministic: encrypting the same message always produces the same ciphertext.
This makes it insecure, as attackers can guess messages or exploit mathematical properties of RSA.
Padding schemes (e.g., PKCS#1 v1.5 or OAEP) add randomness or structured bytes before encryption.
This ensures different ciphertexts for the same plaintext and provides protection against chosen-plaintext or chosen-ciphertext attacks.
Proper padding is essential for RSA’s security in practice.
DES (Data Encryption Standard)
DES is a symmetric-key block cipher standardized in the 1970s by NIST.
It uses a 56-bit key and operates on 64-bit blocks.
Once a global standard, DES is now considered insecure due to its short key length, which makes it vulnerable to brute-force attacks.
3DES (Triple DES)
Triple DES (3DES) is an extension of DES that applies the DES algorithm three times with either two or three different keys.
This increases the effective key length to 112 or 168 bits.
It offered better security than DES but is now deprecated due to its slow performance and known cryptographic weaknesses.
Camellia
Camellia is a modern symmetric-key block cipher developed in Japan by Mitsubishi Electric and NTT.
It offers security and performance comparable to AES, supporting key sizes of 128, 192, and 256 bits.
Camellia is standardized by ISO/IEC and the NESSIE project.
Though less widely used than AES, it is considered secure and suitable for both software and hardware implementations.
TLS (Transport Layer Security)
TLS is a protocol defined by the IETF to secure data during transmission, most notably in HTTPS.
It uses asymmetric encryption for the handshake and key exchange, then switches to symmetric encryption for efficient bulk data encryption.
TLS provides confidentiality, integrity, and authentication for internet communications.
LUKS (Linux Unified Key Setup)
LUKS is the standard format for full disk encryption on Linux, designed by Clemens Fruhwirth.
It provides strong symmetric encryption for protecting data at rest and supports multiple key slots, allowing different passphrases or keys to unlock the same volume.
SSH (Secure Shell)
SSH is a secure remote access protocol invented by Tatu Ylönen in 1995.
It uses asymmetric encryption to authenticate users and symmetric encryption to secure the session once established.
SSH replaced insecure protocols such as Telnet and rlogin and is now the standard for secure remote administration.
FIPS (Federal Information Processing Standards)
FIPS are cryptographic standards defined by NIST for use in U.S. government systems.
FIPS certification ensures that cryptographic algorithms and implementations meet strict security requirements.
It is often required in government, healthcare, and financial sectors to guarantee compliance and trust.
ISO/IEC
ISO (International Organization for Standardization) and IEC (International Electrotechnical Commission) jointly publish international standards for information technology, including cryptography.
These standards ensure interoperability and security across implementations worldwide.
IPSec
IPSec (Internet Protocol Security) is a suite of protocols designed to secure IP communications.
It operates at the network layer, providing encryption, integrity, and authentication for IP packets.
IPSec is widely used for VPNs and site-to-site secure tunnels.
CBC (Cipher Block Chaining)
CBC is a block cipher mode of operation that chains blocks together for added security.
Each plaintext block is XORed with the previous ciphertext block before encryption, preventing identical plaintexts from producing identical ciphertexts.
An Initialization Vector (IV) is required for the first block to ensure uniqueness.
While stronger than ECB, CBC has weaknesses and should be used with caution.
PKCS7
PKCS7 is a padding scheme used in block cipher encryption.
It fills up the last block of plaintext with bytes all set to the value of the number of padding bytes added.
For example, if 4 bytes of padding are needed, the block is filled with 04 04 04 04.
PKCS7 ensures that plaintext lengths align with the cipher’s block size, but improper validation of padding can lead to padding oracle attacks.