[marshray]

I still can't tell if you're joking.

I've seen a possible back door or two in this or that, but nothing like "every crypto system ever".

If you have evidence of a back door in AES, SHA-2, or anything NIST has standardized (other than Dual_EC_DRBG or openly weakened stuff like export SSL) lots of people would like to hear about it.

[william42]

Didn't the NSA actually make DES stronger?

[marshray]

Yes, the story goes that the NSA assisted IBM in its development by tuning the specific values in the S-boxes to be resistant to differential cryptanalysis, which had not yet been publicly discovered.

They also reduced the key length from 64 to 56 bits. I found this suspicious and didn't accept the explanation that those 8 bits were needed for "parity". Yet, respected cryptographers say this actually brings the key size more in line with the effective strength. So those additional 8 bits in the key were not contributing to the security and it improves the "truth in labeling".

Why would they build weaknesses into standard blocks, the biggest consumer of which is the US government itself?

When the NSA had at times insisted on an upper limit for a protocol's security (e.g., export crypto), they usually would require a simple upper limit on the number of secret bits in the key. When they've submitted fixes they tend to be elegant and minimal (e.g. SHA-0 to SHA-1).

[marchdown]

Can you elaborate on the "openly weakened stuff" part?

I don't know much about security, but I am vaguely aware that there were some efforts by various governments to control, regulate, weaponize and even outlaw crypto, but I don't know where these effort have left us. Are there any crypto systems with acknowledged backdoors? Are there any which are not only widely considered to be secure, but are known to have actually prevented three-letter agencies from getting their way?

[oomkiller]

Back in the 90s the US Government prohibited export of SSL stronger than 40 bits. I believe this is what they're referring to.