Distributed computing

Some Performance Issues (from Radu Sion)

• Pentium 4, 3.6 ghz, 1 gigabyte of RAM
• RSA sign: 261/sec; RSA verify: 5324/sec
• Private key (3DES): 26 MB/sec
• Collision free hashing: 200 MB/sec

Secure File System Protocol (David Mazieres)

• Basically, the downloader uses an SSL interaction with the server that downloader trusts.
• That is, downloader encrypts a session private key using that server’s public key.
• So, nobody else can know what downloader requested.
• Not yet solved: how does downloader know this server is validated by author?

Secure File System Protocol key insight

• Each file name is of the form: /sfs/nyu/cs5349874628/dennis/foobar
• The funny number is the SHA-1 hash of the public key of the proper server.
• So, this is the proper server for the file iff the public key of the server Pk when hashed gives cs5349874628.
• Downloader checks this before sending the SSL message which will use Pk.

Secure File System Protocol questions

• What if you lie about your public key?
• How do I discover these strange names?

Secure File System Protocol answers

• What if you lie about your public key?
• You can but then you won’t have the associated private key so won’t be able to respond properly to my SSL request.
• How do I discover these strange names?
• There does have to be one site you trust which has names you believe.

Secure File System Protocol summary

• Downloader goes to trusted name server site.
• Gets name (including funny encrypted part) and maybe other information, e.g. hash of the contents.
• Goes to a server that allegedly holds that file. If server’s public key when hashed equals the funny part of the name, then that server is legitimate.
• So, downloader engages that server in SSL and downloads the file confidentially.