Key length

wikipedia:Key length

• 2048 bits, default for RSA keys in OpenSSH 4.2 (2005)
• 1024 bits
• 512 bits
• 256 bits: ed25519

RSA

• 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

OpenSSH 7.6 (October 2017)

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

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