Allright, I’m stupid. There’s a command-line tool called security that does just this (and lots of other actions on keychains).
An example usage:
security dump-keychain -d login.keychain
This will dump all the data in the login.keychain (the default keychain for a user) as plaintext, including the passwords. You still have to confirm access , but only once for each key, and it’s much faster than (and doesn’t throw weird errors when trying to access certain fields) using AppleScript. And it’s no hack.
Without the -d option, it will dump all the fields except for the password.
The dumped data for a key looks like this (for an internet key; program keys and certificates have other fields, but the format is the same):
keychain: "/Users/<username>/Library/Keychains/login.keychain"
class: "inet"
attributes:
0x00000007 <blob>="tech.slashdot.org (<username for this web login>)"
0x00000008 <blob>=<NULL>
"acct"<blob>="<username for this web login>"
"atyp"<blob>="form"
"cdat"<timedate>=0x32303038303432333038323730355A00 "20080423082705Z\000"
"crtr"<uint32>=<NULL>
"cusi"<sint32>=<NULL>
"desc"<blob>="Kennwort des Web-Formulars"
"icmt"<blob>="default"
"invi"<sint32>=<NULL>
"mdat"<timedate>=0x32303038303432333038323730355A00 "20080423082705Z\000"
"nega"<sint32>=<NULL>
"path"<blob>=<NULL>
"port"<uint32>=0x00000000
"prot"<blob>=<NULL>
"ptcl"<uint32>="http"
"scrp"<sint32>=<NULL>
"sdmn"<blob>=<NULL>
"srvr"<blob>="tech.slashdot.org"
"type"<uint32>=<NULL>
data:
"<the plaintext password for this key>"