|Key sizes||128 bits|
|Block sizes||128 bits|
|Structure||Nested Feistel network|
SEED is a block cipher developed by the Korea Information Security Agency (KISA). It is used broadly throughout South Korean industry, but seldom found elsewhere. It gained popularity in Korea because 40-bit encryption was not considered strong enough, so the Korea Information Security Agency developed its own standard. However, this decision has historically limited the competition of web browsers in Korea, as no major SSL libraries or web browsers supported the SEED algorithm, requiring users to use an ActiveX control in Internet Explorer for secure web sites.
SEED is a 16-round Feistel network with 128-bit blocks and a 128-bit key. It uses two 8 × 8 S-boxes which, like those of SAFER, are derived from discrete exponentiation (in this case, x247 and x251 – plus some "incompatible operations"). It also has some resemblance to MISTY1 in the recursiveness of its structure: the 128-bit full cipher is a Feistel network with an F-function operating on 64-bit halves, while the F-function itself is a Feistel network composed of a G-function operating on 32-bit halves. However the recursion does not extend further because the G-function is not a Feistel network. In the G-function, the 32-bit word is considered as four 8-bit bytes, each of which is passed through one or the other of the S-boxes, then combined in a moderately complex set of boolean functions such that each output bit depends on 3 of the 4 input bytes.
SEED has a fairly complex key schedule, generating its thirty-two 32-bit subkeys through application of its G-function on a series of rotations of the raw key, combined with round constants derived (as in TEA) from the Golden ratio.
NSS software security library in Mozilla's Gecko platform has implemented support for SEED, and Mozilla Firefox as of 3.5.4 supports SEED as a TLS cipher; however, Mozilla decided to drop the support of SEED by default in Firefox 27 and above because support for SEED has not had any practical positive effect in terms of helping South Korea migrate away from ActiveX-based e-commerce, and other browsers are not offering any SEED-based cipher suites. Unlike SEED, Camellia is still supported by Firefox 27 and above. NSS still supports SEED-based cipher suites.
- Gen Kanai (2007-01-26). "The Cost of Monoculture". Retrieved 2007-01-29.
- "Bug 453234 - Support for SEED Cipher Suites to TLS RFC4010". Mozilla. Retrieved 2013-12-01.
- "Bug 478839 - Firefox should support South Korean SEED crypto cipher suites". Retrieved 2009-08-09.
- "Bug 934663 - Change set of cipher suites enabled by default in Gecko to match cipher suite proposal". Retrieved 2013-11-30.
- Brian Smith (2013-08-08). "Proposal to Change the Default TLS Ciphersuites Offered by Browsers". Retrieved 2013-11-30.
- SEED - KISA (Official Site, in Korean)
- SEED official specification document (English)
- RFC 4269: The SEED encryption algorithm (obsoletes RFC 4009)
- RFC 4010: Use of the SEED Encryption Algorithm in Cryptographic Message Syntax (CMS)
- RFC 4162: Addition of SEED Cipher Suites to Transport Layer Security (TLS)
- RFC 4196: The SEED Cipher Algorithm and Its Use with IPsec
- ISO/IEC 18033-3:2010