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SSL/TLS protocol overview

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1.1.2

Change cipher spec protocol

The change cipher spec protocol is used to change the keying material used for encryption

between the client and server. Keying material is raw data that is used to create keys for

cryptographic use. The change cipher spec protocol consists of a single message to tell the

other party in the SSL/TLS session that the sender wants to change to a new set of keys.

The key is computed from the information exchanged by the handshake protocol.

1.1.3

Alert protocol

Alert messages are used to indicate a change in status or an error condition to the peer.

There are a wide variety of alerts to notify the peer of both normal and error conditions.

Alerts are commonly sent when the connection is closed, an invalid message is received, a

message cannot be decrypted, or the user cancels the operation.

1.1.4

Record protocol

The record protocol receives and encrypts data from the higher-layer and delivers it to the

transport layer. As shown in Figure 3, the record protocol takes the data, fragments it into

TLSPlaintext blocks with a size appropriate to the cryptographic algorithm. Then it optionally

compresses (or, for data received, decompresses) the TLSPlaintext, applies a MAC or

HMAC (HMAC is supported only by TLS) to get the hash tag. Finally the TLSCompressed

data and hash tag (and some padding eventually) are concatenated and encrypted (or

decrypted) using the information negotiated during the handshake protocol.

Encryption and hash ensure, respectively, the confidentiality and the integrity of the

plaintext.

Figure 3. Record protocol operations

1.2

Authentication and certificates

SSL/TLS requires a server certificate and, optionally, a client certificate. The digital

certificate certifies the ownership of a public key by the named subject of the certificate, also

known as public key certificates. This allows others parties to rely upon signatures or

assertions made by the private key that corresponds to the public key that is certified.

Digital certificates used in SSL/TLS comply with the X.509 standard (see [8] in References),

which specifies the information required and the formats for public key certificates. In an