Is the SEED blockcipher still secure? I did found an old question which answers exactly this but it is from 2 years ago and i was wondering if there were any changes. I have not been able to find any new information on the cipher and am quite curious seeing as it's extremely fast.

I've tested it against a very fast (fastest I have found so far) AES implementation which took 392μs to encrypt 128 bytes and 400μs to decrypt 128 bytes.

The SEED cipher took 325μs to encrypt the same 128 bytes and 228μs to decrypt. This is enough to make it interesting for me though I still prefer AES since it is more well known and has been through more scrutiny.

Both tests were done with the same CBC method, so there might be some performance to be gained from a better CBC implementation but i think the one i have is already quite good, for those of you who are wondering i'm using the CycloneSSL library on a RX63N board (renesas development board).

So can SEED be trusted? Can i use it for sensitive data?
Short answer: Yes, I'd still trust SEED.

The topic you linked to is from 2013 (2 years) old and for cryptography nearly never any advances will be made for a 15 year old, rarely used cipher after just 2 years.

As the best cryptanalysis only penetrated half of the rounds back then I'd highly doubt there're any advances by now, as this is only a legacy cipher in most systems and hence not a target like AES which is in widespread use.

EDITED TO ADD(1): As pointed correctly in a comment, if you plan to secure data against nations / national intelligence agencies, you can not rely on the security of SEED and therefore must consider using AES(-192/-256) or maybe even multi-encryption with ciphers with different designs (-> SEED &amp; AES &amp; Threefish/ChaCha &amp; Serpent).