SSH

Question 1

What are 3 types of encryption technologies used?

Answer 1

• Symmetrical encryption
• Asymmetrical encryption
• Hashing.

There are two stages to establishing a connection: first both the systems must agree upon encryption standards to protect future communications, and second, the user must authenticate themselves. If the credentials match, then the user is granted access.

Question 2

What is Symmetrical encryption?

Answer 2

Symmetric encryption is a form of encryption where a secret key is used for both encryption and decryption of a message by both the client and the host. Effectively, any one possessing the key can decrypt the message being transferred.

Symmetrical encryption is often called shared key or shared secret encryption.

Symmetric keys are used to encrypt the entire communication during a SSH Session. Both the client and the server derive the secret key using an agreed method, and the resultant key is never disclosed to any third party. The process of creating a symmetric key is carried out by a key exchange algorithm. What makes this algorithm particularly secure is the fact that the key is never transmitted between the client and the host. Instead, the two computers share public pieces of data and then manipulate it to independently calculate the secret key. Even if another machine captures the publically shared data, it won’t be able to calculate the key because the key exchange algorithm is not known

Question 3

What is Asymmetric encryption?

Answer 3

Asymmetrical encryption uses two separate keys for encryption and decryption. These two keys are known as the public key and the private key. Together, both these keys form a public-private key pair.

The public key, as the name suggest is openly distributed and shared with all parties. While it is closely linked with the private key in terms of functionality, the private key cannot be mathematically computed from the public key. The relation between the two keys is highly complex: a message that is encrypted by a machine’s public key, can only be decrypted by the same machine’s private key. This one-way relation means that the public key cannot decrypt its own messages, nor can it decrypt anything encrypted by the private key.

The private key must remain private i.e. for the connection to be secured, no third party must ever know it. The strength of the entire connection lies in the fact that the private key is never revealed, as it is the only component capable of decrypting messages that were encrypted using its own public key.

Question 4

What is hashing encryption?

Answer 4

One-way hashing is another form of cryptography used in Secure Shell Connections. One-way-hash functions differ from the above two forms of encryption in the sense that they are never meant to be decrypted. They generate a unique value of a fixed length for each input that shows no clear trend which can exploited. This makes them practically impossible to reverse.

Hash

It is easy to generate a cryptographic hash from a given input, but impossible to generate the input from the hash. This means that if a client holds the correct input, they can generate the crypto-graphic hash and compare its value to verify whether they possess the correct input.

SSH uses hashes to verify the authenticity of messages. This is done using HMACs, or Hash-based Message Authentication Codes. This ensures that the command received is not tampered with in any way.

While the symmetrical encryption algorithm is being selected, a suitable message authentication algorithm is also selected. This works in a similar way to how the cipher is selected, as explained in the symmetric encryption section.

Each message that is transmitted must contain a MAC, which is calculated using the symmetric key, packet sequence number, and the message contents. It is sent outside the symmetrically encrypted data as the concluding section of the communication packet.