E=encrypt(K,M) - is message M encrypted with key K gives encrypted text E
M=decrypt(K,E) - is encrypted text E decrypted with key K gives message M
KCA−pub,KCA−priv - is the private-public key pair for a certificate authority, such as Verisign
D=MD(F) - MD is a message digest function, applied to file F giving digest D
F - is a file containing Bob’s public key, KBob−pub, and email address, EmailBob
How does the certificate authority, CA, generate a signature S from the file F using the functions above, in order to build a certificate for Bob consisting of file F followed by the signature, S?
this is my answer: Firstly, Bob will need to go to a well-known authority (such as Verisign) to prove who he is using a passport or driving license or something to prove it is him. A public-private key is generated paying a fee and receives a certificate consisting of his public key and a statement of his identity (such as name, email, address etc.) all hashed and signed with the private key of the authenticating company.
Anyone can verify his public key belongs to him by comparing it with the signature decoded with the public key of the authenticator.
Signature Encrypt - ED = encrypt (Kca-pub-bob, MD(F)
Decrypt - MD(F) = decrypt (Kca-private-bob, ED)