How do you reset an iPhone App's Keychain?

As all of the answers so far rely on you knowing the identifiers you want to delete, I would like to submit the following solution that deletes ALL existing keys for the app (iOS only)

Objective-C:

-(void)resetKeychain {    [self deleteAllKeysForSecClass:kSecClassGenericPassword];    [self deleteAllKeysForSecClass:kSecClassInternetPassword];    [self deleteAllKeysForSecClass:kSecClassCertificate];    [self deleteAllKeysForSecClass:kSecClassKey];    [self deleteAllKeysForSecClass:kSecClassIdentity];}-(void)deleteAllKeysForSecClass:(CFTypeRef)secClass {    NSMutableDictionary* dict = [NSMutableDictionary dictionary];    [dict setObject:(__bridge id)secClass forKey:(__bridge id)kSecClass];    OSStatus result = SecItemDelete((__bridge CFDictionaryRef) dict);    NSAssert(result == noErr || result == errSecItemNotFound, @"Error deleting keychain data (%ld)", result);}

Swift 2.2:

func resetKeychain() {    self.deleteAllKeysForSecClass(kSecClassGenericPassword)    self.deleteAllKeysForSecClass(kSecClassInternetPassword)    self.deleteAllKeysForSecClass(kSecClassCertificate)    self.deleteAllKeysForSecClass(kSecClassKey)    self.deleteAllKeysForSecClass(kSecClassIdentity)}func deleteAllKeysForSecClass(secClass: CFTypeRef) {    let dict: [NSString : AnyObject] = [kSecClass : secClass]    let result = SecItemDelete(dict)    assert(result == noErr || result == errSecItemNotFound, "Error deleting keychain data (\(result))")}

Swift 3:

func resetKeychain() {    deleteAllKeysForSecClass(kSecClassGenericPassword)    deleteAllKeysForSecClass(kSecClassInternetPassword)    deleteAllKeysForSecClass(kSecClassCertificate)    deleteAllKeysForSecClass(kSecClassKey)    deleteAllKeysForSecClass(kSecClassIdentity)}func deleteAllKeysForSecClass(_ secClass: CFTypeRef) {    let dict: [NSString : Any] = [kSecClass : secClass]    let result = SecItemDelete(dict as CFDictionary)    assert(result == noErr || result == errSecItemNotFound, "Error deleting keychain data (\(result))")}

KeychainItemWrapper *keychainItem = [[KeychainItemWrapper alloc] initWithIdentifier:@"nameOfYourKeychain" accessGroup:nil];[keychainItem resetKeychainItem];

Much simpler :)

Edit: In response to a question asked below - what is KeychainItemWrapper?

It's a class written by Apple that you can download here: http://developer.apple.com/library/ios/#samplecode/GenericKeychain/Listings/Classes_KeychainItemWrapper_m.html

Add it to your project and then import it where you would like to use it. Then use the code snippet I provided above.

Block-based version of Vegard’s solution:

void (^deleteAllKeysForSecClass)(CFTypeRef) = ^(CFTypeRef secClass) {    id dict = @{(__bridge id)kSecClass: (__bridge id)secClass};    OSStatus result = SecItemDelete((__bridge CFDictionaryRef) dict);    NSAssert(result == noErr || result == errSecItemNotFound, @"Error deleting keychain data (%d)", (int)result);};deleteAllKeysForSecClass(kSecClassGenericPassword);deleteAllKeysForSecClass(kSecClassInternetPassword);deleteAllKeysForSecClass(kSecClassCertificate);deleteAllKeysForSecClass(kSecClassKey);deleteAllKeysForSecClass(kSecClassIdentity);

For those of us who like to just drop code in without having to have helper methods.