Even among protocols that can't, generally, be cracked, there are known limitations. RSA asymmetric encryption with 1024 bit keys—widely used in SSL/TLS connections—can't be broken by a common or garden-variety hacker. Though algorithms for cracking RSA are known, they're out of reach to individuals, because they require massive computational resources. But that's not a problem for the NSA (or any other organizations that have or can afford large supercomputers). Nobody knows with absolute certainty if the NSA has supercomputers that can be used to attack 1024-bit RSA in a reasonable timeframe, but it's certainly well within the realm of possibility.
A big clue as to susceptibility of 1024-bit RSA to cracking can be found in the government's own recommendations. In its SP 800-57 document, NIST, whose responsibilities include
developing standard rules for use of encryption, it says that use of 1024-bit RSA is deprecated through to the end of this year and disallowed subsequently, precisely because it is susceptible to being broken. 2048-bit RSA, in comparison, is approved until 2030 and disallowed thereafter.
SP 800-57 was last revised in 2012, and academic researchers have been saying that 1024-bit RSA is vulnerable
since at least 2007.
