Home > Uncategorized > When dealing with asymmetric key encryption, is RSA 1024-bit enough?

When dealing with asymmetric key encryption, is RSA 1024-bit enough?

I was just asked if a file that’s encrypted with a RSA 1024-bit public key is strong enough now-a-days. One of the public keys we are using is 1024-bit and was issued “in 1996,” so it seemed like a fair question.

I won’t pretend I’m a mathematician, or even a cryptography buff, however, I do know what to ask the internet to find out what the mathematicians and cryptography experts say.

The original search revealed a few old articles discussing that RSA 1024 might have some real world weaknesses, and that it will be defeated shortly. Although the math is solid, it seems that the computing power needed was just theoretical and has yet to be obtainable.

I produced my final answer citing the group with arguably one of the most stringent security policies, the NSA. Simply, the NSA allows RSA encryption be used to protect SECRET level information, with bit strengths 2048 and 3072, or rather:

AES with 128-bit keys provides adequate protection for classified information up to the SECRET level. Similarly, ECDH and ECDSA using the 256-bit prime modulus elliptic curve as specified in FIPS PUB 186-3 and SHA-256 provide adequate protection for classified information up to the SECRET level. Until the conclusion of the transition period defined in CNSSP-15, DH, DSA and RSA can be used with a 2048-bit modulus to protect classified information up to the SECRET level.

As for TOP SECRET:

AES with 256-bit keys, Elliptic Curve Public Key Cryptography using the 384-bit prime modulus elliptic curve as specified in FIPS PUB 186-3 and SHA-384 are required to protect classified information at the TOP SECRET level.

FIPS doesn’t mind 1024, 2048 or 3072 bit RSA, it appears; but the NSA do not like 1024 bit RSA, and the NSA do not like RSA for TOP SECRET info.

FIPS 186-3 covers the details of implementing the encryption, including the hashing functions (check out starting on PDF page 33, or real page 22).

This isn’t to say that 1024 bit encryption is weak, it may just be broken sooner than 2048 and 3072.

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