Well, there's your answer. DSA and SHA-256 are not encryption algorithms, and are not used to hide information. They are used to authenticate data and communications, ie, make sure it hasn't been tampered with and was really created by the person who claims to have created it. The NSA receives data from other US government agencies and foreign governments as well as private companies. The NSA absolutely requires a way for these people providing them data to prove that they really are who they say are and that their data hasn't been tampered with. The only way they can do that is to provide secure public-key cryptosystems and hashing algorithms, and they daren't risk including a backdoor in case an enemy finds it and uses it to feed the NSA false data that appears to come from trusted sources. If these algorithms are flawed, the NSA's whole operation is in jeopardy.