HIGH AI PREVALENCE: MEDIUM auth.go.crypto.weak-cipher

A broken or deprecated block/stream cipher is used to protect data.

CWE-327 OWASP A02:2021 go

Why AI tools produce this: AI coding tools produce this regularly, typically when prompted for a shortcut or a quick fix.

Why this matters

DES (des.NewCipher) and 3DES (des.NewTripleDESCipher) have a 64-bit block and are considered insecure (Sweet32, brute-force), while RC4 (rc4.NewCipher) has well-known keystream biases and is forbidden by RFC 7465. For OAuth/OIDC this means tokens, client secrets, and other sensitive material are not adequately protected and may be recovered by an attacker.

Use authenticated AES instead: load the key with crypto/aes (aes.NewCipher(key)) and wrap it in cipher.NewGCM(block) to get AES-GCM, which provides both confidentiality and integrity.

VULNERABLE

vulnerable.go

package main

import (
	"crypto/cipher"
	"crypto/des"
	"crypto/rc4"
)

// DES is a broken 64-bit block cipher.
func desCipher(key []byte) (cipher.Block, error) {
	// ruleid: auth.go.crypto.weak-cipher
	return des.NewCipher(key)
}

// 3DES is deprecated (Sweet32, 64-bit block).
func tripleDESCipher(key []byte) (cipher.Block, error) {
	// ruleid: auth.go.crypto.weak-cipher
	return des.NewTripleDESCipher(key)
}

// RC4 has well-known keystream biases and is forbidden by RFC 7465.
func rc4Cipher(key []byte) (*rc4.Cipher, error) {
	// ruleid: auth.go.crypto.weak-cipher
	return rc4.NewCipher(key)
}

SAFE

safe.go

package main

import (
	"crypto/aes"
	"crypto/cipher"
)

// ok: auth.go.crypto.weak-cipher -- AES-GCM provides authenticated encryption
func aesGCM(key []byte) (cipher.AEAD, error) {
	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}
	return cipher.NewGCM(block)
}

// ok: auth.go.crypto.weak-cipher -- plain AES block cipher is not flagged
func aesBlock(key []byte) (cipher.Block, error) {
	return aes.NewCipher(key)
}

Suppressing this rule

If a finding is a genuine false positive, scope the suppression to the exact line and leave a reason, never disable the rule project-wide. Disable directives are line-scoped by design.

// oauthlint-disable-next-line auth.go.crypto.weak-cipher -- <reason>

References

https://pkg.go.dev/crypto/aes#NewCipher ↗https://pkg.go.dev/crypto/cipher#NewGCM ↗https://cwe.mitre.org/data/definitions/327.html ↗