Security & Encryption¶

Overview¶

The script provides secure defaults while allowing full customization of the encryption stack.

Default Security Settings¶

Setting	Default Value
Data cipher	AES-128-GCM
Certificate type	ECDSA
ECDSA curve	prime256v1
HMAC digest	SHA256
TLS minimum	1.2
Control channel	tls-crypt-v2
Auth mode	PKI

Data Channel Ciphers¶

The data channel cipher encrypts the actual VPN traffic:

Cipher	Type	Notes
`AES-128-GCM`	AEAD	Default — fast and secure
`AES-192-GCM`	AEAD	—
`AES-256-GCM`	AEAD	Maximum AES security
`AES-128-CBC`	Block	Legacy compatibility
`AES-192-CBC`	Block	Legacy compatibility
`AES-256-CBC`	Block	Legacy compatibility
`CHACHA20-POLY1305`	AEAD	Better on devices without AES-NI (OpenVPN 2.5+)

Tip

AEAD ciphers (GCM, CHACHA20-POLY1305) are recommended. They provide both encryption and authentication in a single operation.

Certificate Configuration¶

Certificate Types¶

ECDSA (default)RSA

Elliptic Curve Digital Signature Algorithm. Faster, lighter, and more secure than RSA for equivalent security levels.

sudo ./openvpn-install.sh install \
  --cert-type ecdsa \
  --cert-curve prime256v1

Available curves:

Curve	Security Level
`prime256v1`	128-bit (default)
`secp384r1`	192-bit
`secp521r1`	256-bit

RSA certificates for legacy client compatibility.

sudo ./openvpn-install.sh install \
  --cert-type rsa \
  --rsa-bits 4096

Available key sizes: 2048, 3072, 4096

Certificate Validity¶

Certificate	Default	Option
Server	3650 days (10 years)	`--server-cert-days`
Client	3650 days (10 years)	`--client-cert-days`
CRL	5475 days (15 years)	—

Server Certificate Name¶

The server certificate name is randomized for privacy. This prevents revealing server identity in the TLS handshake.

TLS Configuration¶

Minimum TLS Version¶

# TLS 1.2 (default — broad compatibility)
sudo ./openvpn-install.sh install --tls-version-min 1.2

# TLS 1.3 (maximum security)
sudo ./openvpn-install.sh install --tls-version-min 1.3

TLS 1.3 Cipher Suites¶

When using TLS 1.3, you can configure the cipher suites:

TLS_AES_256_GCM_SHA384
TLS_AES_128_GCM_SHA256
TLS_CHACHA20_POLY1305_SHA256

sudo ./openvpn-install.sh install \
  --tls-version-min 1.3 \
  --tls-ciphersuites "TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256"

Key Exchange Groups¶

Default: X25519:prime256v1:secp384r1:secp521r1

sudo ./openvpn-install.sh install --tls-groups "X25519:secp384r1"

Control Channel Security¶

The control channel handles key exchange and authentication. Three modes are available:

Mode	Option	Description	Requires
tls-crypt-v2	`--tls-sig crypt-v2`	Per-client encryption keys (default)	OpenVPN 2.5+
tls-crypt	`--tls-sig crypt`	Shared encryption key	OpenVPN 2.4+
tls-auth	`--tls-sig auth`	HMAC authentication only	Any version

tls-crypt-v2 advantages

Each client gets a unique key derived from the server key
Prevents unauthorized clients from initiating TLS handshakes
Provides DDoS protection for the server

Authentication Modes¶

PKI (default)¶

Traditional CA-based authentication with Certificate Revocation Lists (CRL):

sudo ./openvpn-install.sh install --auth-mode pki

Full PKI infrastructure with CA
CRL-based revocation
Suitable for any deployment size

Fingerprint (OpenVPN 2.6+)¶

WireGuard-like peer fingerprint authentication:

sudo ./openvpn-install.sh install --auth-mode fingerprint

Self-signed certificates without CA
Simpler setup for small deployments
Fingerprint-based peer verification
No CRL needed — fingerprints stored in config

Compression¶

Compression is disabled

The script does not enable compression to prevent the VORACLE vulnerability. OpenVPN 2.6+ blocks compression by default.

HMAC Digest¶

The HMAC algorithm used for packet authentication:

Algorithm	Option
SHA256	`--hmac SHA256` (default)
SHA384	`--hmac SHA384`
SHA512	`--hmac SHA512`

Unprivileged Mode¶

The script can configure OpenVPN to run as nobody:nogroup, reducing the attack surface:

Drops root privileges after initialization
Cannot modify system files at runtime