@interface FXKeychain : NSObject
+ (instancetype)defaultKeychain;
@property (nonatomic, copy, readonly) NSString *account;
@property (nonatomic, copy, readonly) NSString *service;
@property (nonatomic, copy, readonly) NSString *accessGroup;
- (id)initWithAccount:(NSString *)account
service:(NSString *)service
accessGroup:(NSString *)accessGroup;
- (BOOL)setObject:(id)object forKey:(id)key;
- (BOOL)setObject:(id)object forKeyedSubscript:(id)key;
- (BOOL)removeObjectForKey:(id)key;
- (id)objectForKey:(id)key;
- (id)objectForKeyedSubscript:(id)key;
@end シンプルでなかなかいい。Subscripting対応なので keychain[@"key"]=obj や obj=keychain[@"Key1"]みたいな書き方ができる（たぶん）。
参考）
