Thin Client Security
Recently there have been a number of proposals for bitcoin clients which do not store a copy of the entire block chain. I will refer to all such clients as "thin clients". This page is meant to be a place to try to make sense of the security and trust implications of the various schemes.
Thin Client Strategies
Simplified Payment Verification
This scheme is described in section 8 of the original bitcoin whitepaper.
BCCAPI
Clients are vulnerable to a double-spend attack against them by the server. Therefore, they are implicitly trusting it.
Electrum
Clients are vulnerable to a double-spend attack against them by the server. Therefore, they are implicitly trusting it.