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ssh-keygen is able to generate a key using one of three different digital signature algorithms. With the help of the ssh-keygen tool, a user can create passphrase keys for any of these key types. To provide for unattended operation, the passphrase can be left empty, albeit at increased risk.
This output would be produced by a ssh-keygen -r host.example.com. command on the target server by reading the existing default SSH host key (Ed25519). [5] With the OpenSSH suite, the ssh-keyscan utility can be used to determine the fingerprint of a host's key; using the -D will print out the SSHFP record directly. [6]
A 2019 draft of "FIPS 186-5" notes the intention to allow usage of Ed25519 [24] for digital signatures. The 2023 update of Special Publication 800-186 allows usage of Curve25519. [25] In February 2017, the DNSSEC specification for using Ed25519 and Ed448 was published as RFC 8080, assigning algorithm numbers 15 and 16. [26]
The original team has optimized Ed25519 for the x86-64 Nehalem/Westmere processor family. Verification can be performed in batches of 64 signatures for even greater throughput. Ed25519 is intended to provide attack resistance comparable to quality 128-bit symmetric ciphers. [9] Public keys are 256 bits long and signatures are 512 bits long. [10]
ssh-add and ssh-agent, utilities to ease authentication by holding keys ready and avoid the need to enter passphrases every time they are used. ssh-keygen, a tool to inspect and generate the RSA, DSA and elliptic-curve keys that are used for user and host authentication. ssh-keyscan, which scans a list of hosts and collects their public keys.
SSH only verifies that the same person offering the public key also owns the matching private key. In all versions of SSH it is important to verify unknown public keys , i.e. associate the public keys with identities , before accepting them as valid.
The signature is valid if , matches Alice's public key. The signature is invalid if all the possible R points have been tried and none match Alice's public key. Note that an invalid signature, or a signature from a different message, will result in the recovery of an incorrect public key.
[1] [2] [3] This shared secret may be directly used as a key, or to derive another key. The key, or the derived key, can then be used to encrypt subsequent communications using a symmetric-key cipher. It is a variant of the Diffie–Hellman protocol using elliptic-curve cryptography.