Key Management For Secure Shell; Generating The Keys - Fujitsu Siemens Computers SX series User Manual

Sx150 business server
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6.4 Key management for Secure Shell

6.4.1 Generating the keys

In SSH authentication and encryption are based on the asymmetrical system of public and
private keys. Encryption and decryption are performed with different keys, and it is not
possible to derive the key for decryption from that for encryption. For this purpose the user
generates a pair consisting of a public and a private key. The public key is intended for
forwarding to other users, while the private key is not forwarded by the user.
The two keys are used as follows:
Authentication
When a user is logged onto a remote system this system generates a random number,
encrypts it with the user's public key, and returns it to the local system. The corre-
sponding private key is required to decrypt this coded random number; the decrypted
date is returned to the remote system and is checked there. This is the way in which the
owner of this private key identifies himself/herself.
The private key enables signatures (e.g. for a digital signature) to be generated. A
signature generated with a private key cannot be forged by anyone who does not own
this key.
Anyone who has the associated public key can verify that a signature is genuine.
Encryption
The public key can also be used to encrypt a message to someone who owns the
associated private key.
Only someone who owns the associated private key can decrypt such a message.
As the public key is only used for encrypting a message, it is not so important to ensure that
it gets into the wrong hands, in contrast to the private key.
U41272-J-Z385-3-76
Key management for Secure Shell
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