ssh-keygen(1) -t rsa -b 4096 -f id-autossh-rsa -q -N ""
authentication key generation, management and conversion
-t type
        Specifies the type of key to create.  The possible values are “rsa1” for protocol version 1 and
        “dsa”, “ecdsa” or “rsa” for protocol version 2.
-b bits
        Specifies the number of bits in the key to create.  For RSA keys, the minimum size is 768 bits and
        the default is 2048 bits.  Generally, 2048 bits is considered sufficient.  DSA keys must be exactly
        1024 bits as specified by FIPS 186-2.  For ECDSA keys, the -b flag determines they key length by
        selecting from one of three elliptic curve sizes: 256, 384 or 521 bits.  Attempting to use bit
        lengths other than these three values for ECDSA keys will fail.
-f filename
        Specifies the filename of the key file.
-q      Silence ssh-keygen.
-N new_passphrase
        Provides the new passphrase.
source manpages: ssh-keygen