nodemcu-firmware/docs/modules/crypto.md

crypto Module

Since	Origin / Contributor	Maintainer	Source
2015-06-02	DiUS, Johny Mattsson	Johny Mattsson	crypto.c

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

The following encryption/decryption algorithms/modes are supported:

• "AES-ECB" for 128-bit AES in ECB mode (NOT recommended)
• "AES-CBC" for 128-bit AES in CBC mode

The following hash algorithms are supported:

• MD5
• SHA1
• SHA256, SHA384, SHA512 (unless disabled in app/include/user_config.h)

crypto.encrypt()

Encrypts Lua strings.

Syntax

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

Parameters

• algo the name of a supported encryption algorithm to use
• 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(encoder.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 a supported encryption algorithm to use
• 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 initialization 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(encoder.toHex(cipher))
print(crypto.decrypt("AES-ECB", key, cipher))

See also

• crypto.encrypt()

crypto.fhash()

Compute a cryptographic hash of a a file.

Syntax

hash = crypto.fhash(algo, filename)

Parameters

• algo the hash algorithm to use, case insensitive string
• filename the path to the file to hash

Returns

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

Example

print(encoder.toHex(crypto.fhash("sha1","myfile.lua")))

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 str string to hash contents of

Returns

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

Example

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

crypto.new_hash()

Create a digest/hash object that can have any number of strings added to it. Object has update and finalize functions.

Syntax

hashobj = crypto.new_hash(algo)

Parameters

algo the hash algorithm to use, case insensitive string

Returns

Userdata object with update and finalize functions available.

Example

hashobj = crypto.new_hash("SHA1")
hashobj:update("FirstString")
hashobj:update("SecondString")
digest = hashobj:finalize()
print(encoder.toHex(digest))

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

Returns

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

Example

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

crypto.new_hmac()

Create a hmac object that can have any number of strings added to it. Object has update and finalize functions.

Syntax

hmacobj = crypto.new_hmac(algo, key)

Parameters

• algo the hash algorithm to use, case insensitive string
• key the key to use (may be a binary string)

Returns

Userdata object with update and finalize functions available.

Example

hmacobj = crypto.new_hmac("SHA1", "s3kr3t")
hmacobj:update("FirstString")
hmacobj:update("SecondString")
digest = hmacobj:finalize()
print(encoder.toHex(digest))

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 encoder.toHex() to get a textual representation of it.

Example

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