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Comment by eboyjr | Hacker News Reader

Just a half-baked idea: If you don't want to make a new request for every connection, and the recipient owns a huge block of IPv6 addresses, the recipient can create an asynchronous key pair where the public key is used as the IPv6 suffix. The United States Department of Defense owns /13. This provides 115 bits of public key information. The sender can use the IPv6 address as the public key.

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115 bits of security is pretty good, for example 3DES, while not exactly a great choice today, is still considered secure and acceptable for use today, with its 112 bits of security. However, I know of no public key encryption scheme that would give acceptable security with only 115 bits of public key. With RSA, you need at least 1024 bits, and probably should rather use 2048. Elliptic curve cryptography is considerably better here, but an ECC key of length n stil gives you only n/2 bits of security, which would be way too little here.

2048 bits of RSA key is the same amount of security as 112 bits of symmentric key, though.

Yes, that’s my point — you need to use 2048 bits for key to get 128 bits of security, so there is no way to fit the public key in the IPv6 address.

Can't you do something with a key-stretching system [0] maybe, to turn 112 bits of IPV6 into 2048 bits of RSA input, though, since you definitely have the right amount of entropy?

0. https://en.wikipedia.org/wiki/Key_stretching

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