Key length

wikipedia:Key length

• 2048 bits
• 1024 bits
• 512 bits
• 256 bits: ed25519

OpenSSH

OpenSSH 7.6 (October 2017)

• Refuse keys length <1024 bits in length and improve reporting for keys that do not meet this requirement.

macOS 10.15 (2019)

requires that TLS server certificates and issuing CAs using RSA keys must use key sizes greater than or equal to 2048.  

• OpenSSH 4.2: September 1, 2005 https://www.openssh.com/txt/release-4.2
  • Increase the default size of new RSA/DSA keys generated by ssh-keygen from 1024 to 2048 bits.

Related

• Openssh client: Invalid key lenght connecting to a Cisco device
• RSA, Ed25519
• ssh-keygen

See also

• Public key cryptography, private key, public key, key length, ssh-keygen, ssh-keyscan, Root certificate, KEX, Generate a key
• OpenSSH (changelog): /etc/ssh/sshd_config | /etc/ssh/ssh_config | ~/.ssh/ | openSSL | sshd logs | sftp | scp | authorized_keys | ssh-keygen | ssh-keyscan | ssh-add | ssh-agent | ssh | Ssh -O stop | ssh-copy-id | CheckHostIP | UseKeychain, OpenSSF
• Public-key cryptography: RSA, DSA, ECDSA, EdDSA (Ed25519), AES, RSA Conference, hash, pkeyutl, Signature, key length, Easyrsa, OAEP, Ron Rivest, Adi Shamir, Leonard Adleman

https://support.apple.com/en-us/HT210176