n2n/doc/CRYPTO.md

Cryptography in n2n

Payload

Overview

Payload encryption currently comes four in different flavors. Supported ciphers are enabled using the indicated command line option:

• Twofish in CBC mode (-A2)
• AES in CBC mode (-A3)
• ChaCha20 (CTR) (-A4)
• SPECK in CTR mode (-A5)

To renounce encryption, -A1 enables the so called null_transform transmitting all data unencrpytedly.

The following quick comparing chart might help make a decision on what cipher to use:

Cipher	Mode	Block Size	Key Size	IV length	Speed	Built-In	Origin
Twofish	CBC	128 bits	128 bit (?)	32 bit	-	Y	Bruce Schneier
AES	CBC	128 bits	128, 192,256 bit	64 bit	O..+	N	Joan Daemen and Vincent Rijmen, NSA-approved
ChaCha20	CTR	Stream	256 bit	128 bit	+..++	N	Daniel J. Bernstein
SPECK	CTR	Stream	256 bit	128 bit	++	Y	NSA

As all block ciphers are used in CBC mode, they require a padding which results in encrypted payload sizes modulo the respective blocksize. Sizewise, this could be considered a disadvantage. On the other hand, stream ciphers need a longer initialization vector (IV) to be transmitted.

Note that AES and ChaCha20 only are available if n2n was compiled with openSSL support while Twofish and SPECK always are available as built-ins.

Twofish

AES

ChaCha20

SPECK

Header

Encryption

Checksum

Replay Protection