add crypto library

doc/en/scripting/builtins/libcrypto.md

@@ -0,0 +1,140 @@
+# *crypto* library
+
+The library provides common cryptographic functions for mods
+
+TLS and HTTP are not part of this library. They can use crypto for expensive
+operations
+
+Keys, signatures, hashes and encrypted data are passed as regular Lua strings.
+Strings may contain zero bytes
+
+The current API version is available in `crypto.API_VERSION`
+
+## Hashing
+
+```lua
+crypto.sha256(data: str) -> str
+crypto.sha384(data: str) -> str
+crypto.sha512(data: str) -> str
+crypto.md5(data: str) -> str
+crypto.hash(hash: str, data: str) -> str
+crypto.hmac(hash: str, key: str, data: str) -> str
+```
+
+Supported names are `SHA256`, `SHA384`, `SHA512` and `MD5`
+
+MD5 is provided for old formats. SHA256 should be used for new data
+
+Large data can be hashed in parts
+
+```lua
+local hash = crypto.hash_new("SHA256")
+hash:update(part1)
+hash:update(part2)
+local result = hash:final()
+```
+
+Call `reset` before using the context again
+
+## Signatures
+
+```lua
+crypto.ed25519_keypair() -> private_key, public_key
+crypto.ed25519_public(private_key: str) -> str
+crypto.ed25519_sign(private_key: str, message: str) -> str
+crypto.ed25519_verify(public_key: str, message: str, signature: str)
+    -> true
+    -> false, error
+
+crypto.ecdsa_keypair(curve: str) -> private_key, public_key
+crypto.ecdsa_public(curve: str, private_key: str) -> str
+crypto.ecdsa_sign(curve: str, private_key: str, message: str, hash: str) -> str
+crypto.ecdsa_verify(curve: str, public_key: str, message: str,
+                    signature: str, hash: str)
+    -> true
+    -> false, error
+
+crypto.rsa_pkcs1_verify(hash: str, modulus: str, exponent: str,
+                        message: str, signature: str)
+    -> true
+    -> false, error
+crypto.rsa_pss_verify(hash: str, modulus: str, exponent: str,
+                      message: str, signature: str, salt_length: int)
+    -> true
+    -> false, error
+```
+
+Ed25519 keys are 32 bytes and signatures are 64 bytes
+
+ECDSA supports `P-256`, `P-384` and `P-521`. Public keys use the uncompressed
+SEC1 format and signatures use DER
+
+RSA modulus and exponent use big endian. A `salt_length` of `-1` uses the hash
+size. RSA key generation is not provided, Ed25519 is easier for new keys
+
+## Key exchange
+
+```lua
+crypto.x25519_keypair() -> private_key, public_key
+crypto.x25519_public(private_key: str) -> str
+crypto.x25519(private_key: str, peer_public_key: str) -> str
+crypto.x25519_shared(private_key: str, peer_public_key: str) -> str
+
+crypto.p256_keypair() -> private_key, public_key
+crypto.p256_public(private_key: str) -> str
+crypto.p256_shared(private_key: str, peer_public_key: str) -> str
+```
+
+`x25519` and `x25519_shared` do the same operation
+
+Pass the shared secret through HKDF before using it as a key
+
+## Encryption
+
+```lua
+crypto.aes_gcm_encrypt(key: str, nonce: str, aad: str, plaintext: str) -> str
+crypto.aes_gcm_decrypt(key: str, nonce: str, aad: str, ciphertext: str)
+    -> plaintext
+    -> nil, error
+
+crypto.chacha20_poly1305_encrypt(key: str, nonce: str, aad: str,
+                                 plaintext: str) -> str
+crypto.chacha20_poly1305_decrypt(key: str, nonce: str, aad: str,
+                                 ciphertext: str)
+    -> plaintext
+    -> nil, error
+```
+
+AES GCM accepts 16 and 32 byte keys
+
+ChaCha20 Poly1305 uses a 32 byte key and a 12 byte nonce
+
+A 16 byte tag is appended to ciphertext. Decryption returns nothing when the
+tag is invalid
+
+Never use the same nonce twice with the same key
+
+## Other functions
+
+```lua
+crypto.random_bytes(length: int) -> str
+crypto.constant_time_equal(left: str, right: str) -> bool
+crypto.hkdf_extract(hash: str, salt: str, ikm: str) -> str
+crypto.hkdf_expand(hash: str, prk: str, info: str, length: int) -> str
+crypto.pbkdf2(hash: str, password: str, salt: str,
+              iterations: int, length: int) -> str
+crypto.scrypt(password: str, salt: str, n: int, r: int, p: int,
+              length: int, [optional]max_memory: int=0) -> str
+crypto.features() -> table
+```
+
+Use scrypt or PBKDF2 with a random salt for passwords. A regular SHA256 hash is
+not suitable for password storage
+
+`features` returns the OpenSSL version and available functions
+
+An invalid signature returns `false, "invalid_signature"`
+
+An invalid encryption tag returns `nil, "authentication_failed"`
+
+Invalid arguments raise a regular Lua error