Encryption

Key Management

SSH Key Management

Key Creation

As of December 2015, the most secure key type is ed25519 with 4096-bit:

ssh-keygen -t ed25519 -b 4096 -C my@email.com -f keyfile

Older clients may not support ed25519, but fuck them.

Secure Configuration

Using crypto is only the first step. You need to ensure that the tools you use are locked down to enforce only the protocols that are not known to be weak.

SSH

Server Config

Ciphers

As of 2015-12-04, the best Ciphers setting in /etc/ssh/sshd_config is:

Ciphers aes192-ctr,aes256-ctr,arcfour256,aes256-gcm@openssh.com,chacha20-poly1305@openssh.com,arcfour

MACs

As of 2015-12-04, the best MACs setting in /etc/ssh/sshd_config is:

• Disable anything using MD5
• Disable anything using less than 128 bits
• Disable anything not using -etm mode

Use the following config file:

MACs hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-ripemd160-etm@openssh.com,umac-64-etm@openssh.com,umac-128-etm@openssh.com

SSL/TLS Key Management

Key Creation

If you need a SSL/TLS cert that is signed by a root authority for public use in a web browser or other SSL/TLS client, use Let’s Encrypt to get free SSL certificates.
Let’s Encrypt is a new Certificate Authority: It’s free, automated, and open. In Public Beta 2015-12-03.

Secure SSL/TLS Ciphers

See https://www.owasp.org/index.php/TLS_Cipher_String_Cheat_Sheet

Stunnel

As of 2018-07-02, using TLS 1.3 with stunnel, this is the most secure configuration (TLS 1.2 and 1.3 only):

verify = 2
sslVersion = all
options = NO_SSLv3
options = NO_TLSv1
options = NO_TLSv1.1
options = CIPHER_SERVER_PREFERENCE
options = DONT_INSERT_EMPTY_FRAGMENTS
ciphers = TLS13-AES-256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:DHE-RSA-AES256-GCM-SHA384

Apache

As of 2018-07-02, using TLS 1.2 with apache, this is the most secure configuration (TLS 1.2 only):

SSLEngine On
SSLProtocol TLSv1.2
SSLHonorCipherOrder On
SSLProtocol -ALL +TLSv1.2
SSLCipherSuite "ECDHE-RSA-AES256-GCM-SHA384 ECDHE-RSA-AES128-GCM-SHA256 DHE-RSA-AES256-GCM-SHA384 DHE-RSA-AES128-GCM-SHA256 !ECDHE-RSA-AES256-SHA384 !ECDHE-RSA-AES128-SHA256 !ECDHE-RSA-AES256-SHA !ECDHE-RSA-AES128-SHA !DHE-RSA-AES256-SHA256 !DHE-RSA-AES256-SHA !DHE-RSA-AES128-SHA256 !DHE-RSA-AES128-SHA"

# Enable HSTS
Header always set Strict-Transport-Security "max-age=63072000; includeSubdomains;"