| 6.5 |  | Digital Certificates |
| 6.5.1 |  | Overview |

| This section presents an overview of Cisco IOS CA support. Cisco IOS supports the following open CA standards :

- Internet Key Exchange (IKE) is a hybrid protocol that implements Oakley and Skeme key exchanges inside the ISAKMP framework. While IKE can be used with other protocols, its initial implementation is with the IPSec protocol. IKE provides authentication of the IPSec peers, negotiates IPSec keys, and negotiates IPSec security associations.
- Public-Key Cryptography Standard #7 (PKCS #7) is a standard from RSA Data Security, Inc. used to encrypt, sign, and package certificate enrollment messages.
- Public-Key Cryptography Standard #10 (PKCS#10) A standard syntax from RSA Data Security, Inc. for certificate requests.
- RSA keys RSA is the public key cryptographic system developed by Ron Rivest, Adi Shamir, and Leonard Adleman. RSA keys come in pairs.The pairs consist of, one public key and one private key .
- X.509v3 certificates Certificate support that allows the IPSec-protected network to scale by providing the equivalent of a digital ID card to each device. When two devices wish to communicate, they exchange digital certificates to prove their identity, thus removing the need to manually exchange public keys with each peer or to manually specify a shared key at each peer. These certificates are obtained from a CA. X.509 as part of the X.500 standard.
- CA Interoperability CA interoperability permits Cisco IOS devices and CAs to communicate so that Cisco IOS devices can obtain and use digital certificates from the CA. Although IPSec can be implemented on a network without the use of a CA, using a CA with SCEP provides manageability and scalability for IPSec.

The other way of authenticating IKE peers is the use of RSA encryption or RSA signatures authentication. The RSA authentication methods are considered more trusted than pre-shared secret authentication, but are also more complex to implement, and are also much slower performers. Both RSA authentication methods are based on the RSA cryptosystem. Peers will prove their identity by proving their possession of the correct private key, which is associated with a certain public key. The other end always needs to have the corresponding public key available locally, to verify the authenticating peer’s data. IKE peer authentication using RSA signatures, works in the following manner (the description is simplified for clarity):

1. Peer A sends some data to peer B and requests it to be signed with peer B’s private key.
2. Peer B signs the received data with its private key.
3. Peer B sends the signed data back to peer A.
4. Peer A verifies the signature with peer B’s public key. If the signature is verified, then peer B is authenticated to peer A.
5. Now peer B sends some data to peer A and requests it to be signed with peer A’s private key.
6. Peer A signs the received data with its private key.
7. Peer A sends the signed data back to peer B.
8. Peer B verifies the sign with peer A’s public key. If the signature is verified, then Peer A is authenticated to peer B.

When both peers authenticate each other, the peer authentication procedure is complete.

IKE peer authentication with RSA signatures is slower than the RSA-encryption authentication method. RSA signatures authentication requires more RSA operations, but also enables non-repudiation of IKE sessions, because digital signing is involved. Usually, the RSA signatures method is used with certificates and an underlying PKI (Public Key Infrastructure), which enable scalability and easier management of keying material in large networks.