nodemcu-firmware/docs/en/modules/crypto.md

crypto Module

The crypto modules provides various functions for working with cryptographic algorithms.

crypto.encrypt()

Encrypts Lua strings.

Syntax

crypto.encrypt(algo, key, plain [, iv])

Parameters

• algo the name of the encryption algorithm to use, one of
  • "AES-ECB" for 128-bit AES in ECB mode
  • "AES-CBC" for 128-bit AES in CBC mode
• key the encryption key as a string; for AES encryption this MUST be 16 bytes long
• plain the string to encrypt; it will be automatically zero-padded to a 16-byte boundary if necessary
• iv the initilization vector, if using AES-CBC; defaults to all-zero if not given

Returns

The encrypted data as a binary string. For AES this is always a multiple of 16 bytes in length.

Example

print(crypto.toHex(crypto.encrypt("AES-ECB", "1234567890abcdef", "Hi, I'm secret!")))

See also

• crypto.decrypt()

crypto.decrypt()

Decrypts previously encrypted data.

Syntax

crypto.decrypt(algo, key, cipher [, iv])

Parameters

• algo the name of the encryption algorithm to use, one of
  • "AES-ECB" for 128-bit AES in ECB mode
  • "AES-CBC" for 128-bit AES in CBC mode
• key the encryption key as a string; for AES encryption this MUST be 16 bytes long
• cipher the cipher text to decrypt (as obtained from crypto.encrypt())
• iv the initilization vector, if using AES-CBC; defaults to all-zero if not given

Returns

The decrypted string.

Note that the decrypted string may contain extra zero-bytes of padding at the end. One way of stripping such padding is to use :match("(.-)%z*$") on the decrypted string. Additional care needs to be taken if working on binary data, in which case the real length likely needs to be encoded with the data, and at which point :sub(1, n) can be used to strip the padding.

Example

key = "1234567890abcdef"
cipher = crypto.encrypt("AES-ECB", key, "Hi, I'm secret!")
print(crypto.toHex(cipher))
print(crypto.decrypt("AES-ECB", key, cipher))

See also

• crypto.encrypt()

crypto.hash()

Compute a cryptographic hash of a Lua string.

Syntax

hash = crypto.hash(algo, str)

Parameters

algo the hash algorithm to use, case insensitive string

Supported hash algorithms are:

• MD2 (not available by default, has to be explicitly enabled in app/include/user_config.h)
• MD5
• SHA1
• SHA256, SHA384, SHA512 (unless disabled in app/include/user_config.h)

Returns

A binary string containing the message digest. To obtain the textual version (ASCII hex characters), please use crypto.toHex().

Example

print(crypto.toHex(crypto.hash("sha1","abc")))

crypto.hmac()

Compute a HMAC (Hashed Message Authentication Code) signature for a Lua string.

Syntax

signature = crypto.hmac(algo, str, key)

Parameters

• algo hash algorithm to use, case insensitive string
• str data to calculate the hash for
• key key to use for signing, may be a binary string

Supported hash algorithms are:

• MD2 (not available by default, has to be explicitly enabled in app/include/user_config.h)
• MD5
• SHA1
• SHA256, SHA384, SHA512 (unless disabled in app/include/user_config.h)

Returns

A binary string containing the HMAC signature. Use crypto.toHex() to obtain the textual version.

Example

print(crypto.toHex(crypto.hmac("sha1","abc","mysecret")))

crypto.mask()

Applies an XOR mask to a Lua string. Note that this is not a proper cryptographic mechanism, but some protocols may use it nevertheless.

Syntax

crypto.mask(message, mask)

Parameters

• message message to mask
• mask the mask to apply, repeated if shorter than the message

Returns

The masked message, as a binary string. Use crypto.toHex() to get a textual representation of it.

Example

print(crypto.toHex(crypto.mask("some message to obscure","X0Y7")))

crypto.toBase64()

Provides a Base64 representation of a (binary) Lua string.

Syntax

b64 = crypto.toBase64(binary)

Parameters

binary input string to Base64 encode

Return

A Base64 encoded string.

Example

print(crypto.toBase64(crypto.hash("sha1","abc")))

crypto.toHex()

Provides an ASCII hex representation of a (binary) Lua string. Each byte in the input string is represented as two hex characters in the output.

Syntax

hexstr = crypto.toHex(binary)

Parameters

binary input string to get hex representation for

Returns

An ASCII hex string.

Example

print(crypto.toHex(crypto.hash("sha1","abc")))