Suppose that A has obtained a certificate from certification authority X1 and B has obtained certificate authority from CA X2. A can use a chain of certificates to obtain B’s public key. In notation of X.509, this chain is represented in the correct order as –

• A. X2 X1 X1 B
• B. X1 X1 X2 A
• C. X1 X2 X2 B
• D. X1 X2 X2 A