SEED Encryption/Decryption
Online SEED encryption/decryption tool, Korean standard 128-bit block cipher, supporting CBC, ECB, CFB, OFB modes.
Algorithm Info
Note: SEED uses a fixed 128-bit key
Note: Supports ECB, CBC, CFB, and OFB modes
Mode & Padding
About SEED Cipher
SEED is a block cipher developed by the Korea Internet & Security Agency (KISA) in 1998. It is used broadly in South Korea and was adopted as a national standard (TTA Standard), and subsequently ISO/IEC 18033-3 and RFC 4269.
| Algorithm | SEED |
| Standard | KISA / ISO 18033-3 / RFC 4269 |
| Key Size | 128 bits (fixed) |
| Block Size | 128 bits |
| Rounds | 16 |
| Mode | ECB / CBC / CFB / OFB |
| Padding | PKCS7 / Zero / ISO10126 / ANSI X.923 / None |
| Origin | Korea (KISA) |
| Year | 1998 |
Features
128-bit fixed key length - simple and secure
128-bit block size - same as AES
16-round Feistel network
Modified Feistel structure using two 64-bit half-blocks
Resistant to known cryptanalytic attacks
Common Use Cases
Financial transaction security in Korea
Government document encryption
SSL/TLS cipher suites (TLS_RSA_WITH_SEED_CBC_SHA)
IPsec VPN encryption
Secure communication applications
Security Notes
SEED has undergone extensive cryptanalysis and is considered secure
Always use random, unpredictable keys and IVs
Never reuse the same Key-IV pair
CBC mode requires correct padding handling
For new international applications, consider ARIA or AES