Here is a method for updating SSH private keys to work with OS X 10.9 Mavericks, using Terminal commands.

cd /Users/nameofuser/.ssh
cp id_rsa{,.bak}
chmod +w id_rsa id_rsa.pub
openssl rsa -in id_rsa -out id_rsa # decrypt in place
openssl rsa -in id_rsa -aes256 -out id_rsa # encrypt in place
ssh-keygen -y -f id_rsa > id_rsa.pub # regen public key
chmod 400 id_rsa id_rsa.pub

The source of this hint.

[crarko adds: I haven’t tested this one. At least not yet. The solution seems to come from a question asked on StackExchange.]

Source: Mac OSX Hints