peass-ng/PEASS-ng · error · ArgumentException

BLAKE2s digest bit length must be a multiple of 8 and not gr

Error message

BLAKE2s digest bit length must be a multiple of 8 and not greater than 256

What it means

The Blake2sDigest(int digestBits) constructor requires the digest size in BITS to be between 8 and 256 inclusive and a multiple of 8; anything else throws this ArgumentException. This enforces BLAKE2s's maximum 256-bit (32-byte) output, half of BLAKE2b's limit.

Source

Thrown at winPEAS/winPEASexe/winPEAS/3rdParty/BouncyCastle/crypto/digests/Blake2sDigest.cs:158

        {
            this.bufferPos = digest.bufferPos;
            this.buffer = Arrays.Clone(digest.buffer);
            this.keyLength = digest.keyLength;
            this.key = Arrays.Clone(digest.key);
            this.digestLength = digest.digestLength;
            this.chainValue = Arrays.Clone(digest.chainValue);
            this.personalization = Arrays.Clone(digest.personalization);
        }

        /**
         * BLAKE2s for hashing.
         *
         * @param digestBits the desired digest length in bits. Must be a multiple of 8 and less than 256.
         */
        public Blake2sDigest(int digestBits)
        {
            if (digestBits < 8 || digestBits > 256 || digestBits % 8 != 0)
                throw new ArgumentException("BLAKE2s digest bit length must be a multiple of 8 and not greater than 256");

            buffer = new byte[BLOCK_LENGTH_BYTES];
            keyLength = 0;
            digestLength = digestBits / 8;
            Init();
        }

        /**
         * BLAKE2s for authentication ("Prefix-MAC mode").
         * <p/>
         * After calling the doFinal() method, the key will remain to be used for
         * further computations of this instance. The key can be overwritten using
         * the clearKey() method.
         *
         * @param key a key up to 32 bytes or null
         */
        public Blake2sDigest(byte[] key)
        {

View on GitHub (pinned to 53fb989abc)

Solutions

1. Pass a multiple of 8 between 8 and 256 (e.g. 256 for the default 32-byte digest)
2. Divide byte sizes by nothing but multiply bits: bytes * 8, capped at 256
3. Use the parameterless Blake2sDigest() for the standard 256-bit digest

Example fix

// before
var d = new Blake2sDigest(512); // copied from Blake2b code
// after
var d = new Blake2sDigest(256); // BLAKE2s max = 256 bits

bool IsValidBlake2sBits(int bits) => bits >= 8 && bits <= 256 && bits % 8 == 0;

When it happens

Trigger: new Blake2sDigest(bits) where bits < 8, bits > 256, or bits % 8 != 0 (e.g. Blake2sDigest(512), common when migrating from BLAKE2b).

Common situations: Confusing bits with bytes (passing 32 expecting 32-byte digest — that is only 32 bits, which is valid, but passing 512 after copying BLAKE2b code is invalid), copying BLAKE2b constructor calls.

Related errors

• BLAKE2b digest bit length must be a multiple of 8 and not gr
• Invalid digest length (required: 1 - 64)
• Keys > 32 are not supported
• Invalid digest length (required: 1 - 32)
• Salt length must be exactly 8 bytes

AI-assisted analysis of peass-ng/PEASS-ng@53fb989abc (2026-09-02). Data as JSON: /api/errors/a82f61b830594d1d. Report an issue: GitHub.