I tried with data from http://dev.twitter.com/pages/xauth:
(function() { var secret = "5kEQypKe7lFHnufLtsocB1vAzO07xLFgp2Pc4sp2vk&"; var access_token = "oauth_consumer_key=sGNxxnqgZRHUt6NunK3uw" + "&oauth_nonce=WLxsobj4rhS2xmCbaAeT4aAkRfx4vSHX4OnYpTE77hA" + "&oauth_signature_method=HMAC-SHA1" + "&oauth_timestamp=1276101652" + "&oauth_version=1.0" + "&x_auth_mode=client_auth" + "&x_auth_password=%&123!aZ+()456242134" + "&x_auth_username=tpFriendlyGiant"; var base_string = "POST&" + encodeURIComponent( "https://api.twitter.com/oauth/access_token") + "&" + encodeURIComponent(access_token); console.debug("base_string", base_string); console.debug("oauth_signature", b64_hmac_sha1(secret, base_string)); })(); This is my base_string: POST&https%3A%2F%2Fapi.twitter.com%2Foauth %2Faccess_token&oauth_consumer_key=sGNxxnqgZRHUt6NunK3uw&oauth_nonce=WLxsobj4rhS2xmCbaAeT4aAkRfx4vSHX4OnYpTE77hA&oauth_signature_method=HMAC- SHA1&oauth_timestamp=1276101652&oauth_version=1.0&x_auth_mode=client_auth&x_auth_password= %25&123!aZ+()456242134&x_auth_username=tpFriendlyGiant This on is from dev.twitter.com POST&https%3A%2F%2Fapi.twitter.com%2Foauth %2Faccess_token&oauth_consumer_key%3DsGNxxnqgZRHUt6NunK3uw %26oauth_nonce%3DWLxsobj4rhS2xmCbaAeT4aAkRfx4vSHX4OnYpTE77hA %26oauth_signature_method%3DHMAC-SHA1%26oauth_timestamp %3D1276101652%26oauth_version%3D1.0%26x_auth_mode%3Dclient_auth %26x_auth_password%3D%2525%2526123%2521aZ%252B %2528%2529456242134%26x_auth_username%3DtpFriendlyGiant I found the differences in encoding %&123!aZ+() prefix from password in base_string: >From dev.twitter.com/pages/xauth: %2525%2526123%2521aZ%252B%2528%2529 >From code above: %25%26123!aZ%2B() I use wrong encoding method then and encoding is wrong applied? BR, Michał Łowicki -- Twitter developer documentation and resources: http://dev.twitter.com/doc API updates via Twitter: http://twitter.com/twitterapi Issues/Enhancements Tracker: http://code.google.com/p/twitter-api/issues/list Change your membership to this group: http://groups.google.com/group/twitter-development-talk?hl=en