Macos – Generating certificate signing request in Keychain Access: which private key is used

There are several keychains on your system:

sudo security list-keychains
"/Users/JonDoe/Library/Keychains/login.keychain"
"/Library/Keychains/System.keychain"

I think you imported it into the System-Keychain: First make a backup of your System Root Certificates before making any changes (or any other keychain you choose):

cd /System/Library/Keychains/
sudo cp SystemRootCertificates.keychain SystemRootCertificates.keychain.old

List all keychains / all certificates in your keychain:

ls -l /System/Library/Keychains/
sudo security dump-keychain /System/Library/Keychains/SystemRootCertificates.keychain

With the second command each certificate of the keychain is shown. Identify the certificate you want to remove. Then remove the certificate with the following command:

sudo security delete-certificate -Z <SHA-1 hash of certificate> /System/Library/Keychains/SystemRootCertificates.keychain
**alternative:**
sudo security delete-certificate -c <common name of certificate> /System/Library/Keychains/SystemRootCertificates.keychain

That's all. Now you can import your certificate again. In case of an error, you can restore your keychain with the following command:

sudo security import certificate_files_backup -k /System/Library/Keychains/SystemRootCertificates.keychain -t cert

The following code worked for me:

NSMutableDictionary *query = [[NSMutableDictionary alloc] init]; 
[query setObject:(id)kSecClassKey forKey:(id)kSecClass]; 
[query setObject:(id)kSecAttrAccessibleWhenUnlocked forKey:(id)kSecAttrAccessible]; 
[query setObject:[NSNumber numberWithBool:YES] forKey:(id)kSecReturnData];

//adding access key 
[query setObject:(id)key forKey:(id)kSecAttrApplicationTag];


//removing item if it exists 
SecItemDelete((CFDictionaryRef)query);

//setting data (private key) 
[query setObject:(id)data forKey:(id)kSecValueData];

CFTypeRef persistKey; OSStatus status = SecItemAdd((CFDictionaryRef)query, &persistKey);

if(status) {
    NSLog(@"Keychain error occured: %ld (statuscode)", status);
    return NO; 
}