There are very few resources for Blake2b apart from the official documentation and website. I would like to know if Blake2b is not vulnerable to length extension attacks unlike SHA2. I would like your help as soon as possible.
All from the BLAKE2 paper BLAKE2: simpler, smaller, fast as MD5
First of all
BLAKE2b is optimized for 64-bit platforms — including NEON-enabled ARMs — and produces digests of any size between 1 and 64 bytes.
and from the abstract of the article
BLAKE2 is often faster than MD5, yet provides security similar to that of SHA-3: up to 256-bit collision resistance, immunity to length extension, indifferentiability from a random oracle, etc
The reason for the resistance to length extension attack
The countermeasure comes from the compression function. The last parameter is set to false when the processed chunk is not the last one.
Compress(h, chunk, cBytesCompressed, false)
It is set to true when the last chunk is compressed.
Compress(h, chunk, cBytesCompressed, true)
So, if an attacker tries to extend a hash, during the recalculation the verifier will arrive in a different hash value then the attackers provided.