client.m

    S3ObjectRequest *thumbReq = [S3ObjectRequest PUTRequestForData:thumbJPEG 
                                                        withBucket:@"teleportd-data" 
                                                               key:[NSString stringWithFormat:@"/%d-%d/%@.jpg", 
                                                                    (dnow / 86400), (dnow % 86400) / 3600,
                                                                    thumbSHA1, nil]];

    //...

    PipeMsg *thumbMsg = [PipeMsg msgWithType:PipeMsgType2w 
                                      target:[NSString stringWithFormat: @"user.%@", [Pipe user], nil] 
                                     subject:@"ACC:S3SIGN" 
                                        body:[NSDictionary dictionaryWithObject:[thumbReq stringToSign]
                                                                         forKey:@"strsign"]];

server.js

    var secretKey = 'XXX';

    var hmac = require('crypto').createHmac("sha1", secretKey);
    hmac.update('' + my.action.body().strsign);
    var sign = hmac.digest(encoding='base64');