Investiga un poco el diccionario de datos de SQLServer, ahí esta toda la información!... navegando muy poquito encontré esto:
Código SQL
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SELECT keys.xtype, keys.name, syscolumns.name, sysindexkeys.indid, sysobjects.type
FROM syscolumns
LEFT JOIN sysobjects ON syscolumns.id = sysobjects.id
LEFT JOIN sysindexkeys ON (syscolumns.id = sysindexkeys.id AND
syscolumns.colid = sysindexkeys.colid)
JOIN sysobjects keys on keys.parent_obj = sysindexkeys.id
WHERE sysobjects.name = 
TableName
AND keys.type = 'K'
AND sysindexkeys.indid IS NOT NULL
ORDER BY keys.id, sysindexkeys.indid, sysindexkeys.keyno
PD: Que raro que me suena "llaves"!
Saludos!