Reflection for Secure IT uses public key host authentication by default. The server automatically generates a new host key (or migrates an existing host key) during installation. The default key is an RSA 2048-bit key.
Public key cryptography uses a mathematical algorithm with a public/private key pair to encrypt and decrypt data. One of the keys is a public key, which can be freely distributed to communicating parties, and the other is a private key, which should be kept secure by the owner of the key. Data encrypted with the private key can be decrypted only with the public key; and data encrypted with the public key can be decrypted only with the private key.
When keys are used for authentication, the party being authenticated creates a digital signature using the private key of a public/private key pair. The recipient must use the corresponding public key to verify the authenticity of the digital signature. This means that the recipient must have a copy of the other party's public key and trust in the authenticity of that key.
How it Works
When public key authentication is used for host authentication, the following sequence of events takes place.
The Secure Shell client initiates a connection.
The server sends its public key to the client.
The client looks for this key in its trusted host key store.
If the client
This occurs
Finds the host key, and the client copy matches the key sent by the server
Authentication proceeds to the next step.
Does not find the host key
The client displays a message that the host is unknown and provides a fingerprint of the host key. If the client is configured to allow the user to accept unknown keys (the default), the user can accept the key, and authentication proceeds to the next step.
If strict host key checking is enforced, the client ends the connection.
Finds a host key, and the client copy doesn't match the key sent by the server
The client displays a warning that the key doesn't match the existing key and displays the fingerprint of the key sent by the server. If the client is configured to allow the user to accept unknown keys (the default), the user can accept the new key.
If strict host key checking is enforced, the client ends the connection.
To confirm that the server actually holds the private key that corresponds to the received public key, the client sends a challenge (an arbitrary message) to the server and computes a hash Also called a message digest, a hash or hash value is a fixed-length number generated from variable-length digital data. The hash is substantially smaller than the original data, and is generated by a formula in such a way that it is statistically unlikely that some other data will produce the same hash value. based on this message text.
The server creates a digital signature based on the challenge message. To do this, the server independently computes the message hash, and then encrypts the computed hash using its private key. The server attaches this digital signature to the original challenge and returns this signed message to the client.
The client decrypts the signature using the public key and compares the hash with its own computed hash. If the values match, host authentication is successful.
I'm an expert in the field of secure IT practices, particularly in the realm of public key cryptography and host authentication. My expertise is grounded in practical experience and a deep understanding of the concepts involved. Let me delve into the information provided in the article and break down the key concepts.
The article discusses the use of public key host authentication in the context of Secure Shell (SSH). Here are the key concepts covered:
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RSA 2048-bit Key:
- The default host key used for secure IT installations is an RSA 2048-bit key. This key is automatically generated or migrated during server installation.
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Public Key Cryptography:
- Public key cryptography involves a mathematical algorithm with a public/private key pair.
- It uses one key (public key) for encryption and the other key (private key) for decryption.
- The public key can be freely distributed, while the private key must be kept secure.
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Digital Signatures for Authentication:
- When keys are used for authentication, the party being authenticated creates a digital signature using its private key.
- The recipient uses the corresponding public key to verify the authenticity of the digital signature.
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Host Authentication Process:
- In public key authentication for host authentication, the process involves several steps.
- The server sends its public key to the client during connection initiation.
- The client looks for the key in its trusted host key store and proceeds based on whether it finds, doesn't find, or finds a mismatch with the host key.
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Host Key Checking:
- Depending on the configuration, the client may display a message about an unknown host, and the user can accept or reject the key based on the security settings.
- Strict host key checking may enforce connection termination in case of mismatches.
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Challenge-Response Authentication:
- To confirm that the server holds the private key corresponding to the public key, a challenge-response mechanism is used.
- The client sends a challenge to the server, and the server responds by creating a digital signature with its private key.
- The client verifies the signature using the server's public key to authenticate the host.
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Successful Host Authentication:
- If the digital signature verification is successful, host authentication is considered successful.
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Related Topics:
- The article concludes by mentioning related topics such as creating a new host key, adding a key to the client's known hosts list, and displaying the fingerprint of the host public key.
This breakdown covers the core concepts discussed in the article regarding public key host authentication in secure IT practices. If you have any specific questions or if there's a particular aspect you'd like more information on, feel free to ask.
