Transport security concepts: Start here

This sub-book presents and defines transfer security concepts that are referred to further in this document, as well as how these security items work. It is comprised of the following topics:

File transfer security is based on the following three principles, as described in this topic:

These three forms of security are independent and must be combined to get a high level of security.

Additionally, the following two security related subjects are described:


Privacy, also referred to as confidentiality, consists in protecting data from being revealed to parties it was not meant for. As a rule, this is accomplished by ciphering transferred data.

Two different cryptographic techniques are often used and combined:

Symmetrical encryption

Symmetrical encryption consists in using a unique key to encrypt and decrypt a message. Both connected parties then share a key that is used to encrypt and decrypt data. The task of privately choosing the key before ciphering data is more problematic as the connected parties share a single key that cannot be clearly transmitted to others.

Symmetrical encryption

View of symetrical key

Asymmetrical encryption

Asymmetrical encryption consists in having a pair of keys where each key by itself can decrypt messages ciphered using the other key. This technique solves the problem of exchanging the key between connected parties. When two parties want to communicate using this encryption mechanism, each party publishes one of its keys and keeps the other one secret.

When using SSL or TLS protocols, a symmetric encryption mechanism is used to cipher data (DES, triple DES, RC2, RC4, and AES). A key used by that mechanism is generated for each session and exchanged during the handshake phase. They are transmitted using an asymmetrical encryption mechanism, which is slower but more secure (RSA) than a symmetric encryption mechanism.

Asymmetrical encryption

View of public and private key encryption


Integrity consists in assuring that the received data has not been altered or modified. Generally, integrity checking is done by adding to the sent data an abstract of that data. When receiving a message, the receiver makes an abstract of the message and compares it with the one sent. If the abstracts match, message integrity is assumed to be correct. Otherwise, it is not.

The message abstract is commonly called the message digest or the hash code. The procedure used to create that hash code is called the digest function or the hash function.

When using SSL or TLS, a hash code, called MAC (Message Authentication Code), is added to each message sent. The standard hash functions used are SHA-1 or MD5.

Hash function


Authentication is the process of verifying a claimed identity. The most widely used authentication mechanisms are:

  • Password request
  • Proof request

Password requests are associated with user login requests. When you have sent a login name, you are then prompted for your password.

Proof requests are associated with asymmetrical encryption mechanisms. After you have sent your public key, or any information relevant enough to get the public key, such as a certificate, you are sent a random encrypted message. If you can decrypt the message, your identity is verified because you own the unique private key associated with the public key.

Proof request

When you use TLS and SSL protocols, the client encrypts the symmetrical key with the server’s public key. If the server can decrypt the key, the client is recognized. Otherwise, dialog is not possible and the connection is closed. When requested, the server authenticates the client through a signature process.


Signing messages is a technique that mixes both integrity and authentication. It consists in sending a ciphered hash code with the message.

When receiving a signed message, both the sender identity and data integrity are verified by decrypting the signature and comparing the result with the calculated hash code. If the hash code is correct, data integrity is accepted, and the sender is as claimed because he had the correct key to encrypt the digest.

Integrity and authentication


Log messages enable you to monitor secure transfer sessions.

The following two messages indicate whether the SSL option was applied when starting up the monitor. Remember that SSL is a protection key option.

CFTI18I SSL Protocol Option is authorized
CFTI25I Init complete _ Security active [ SSL ]

Other messages are used to notify you of secure sessions that have been opened/closed and the parameters negotiated.

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