@consento/crypto
Crypto functionality used in Consento
Last updated 2 days ago by leichtgewicht .
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@consento/crypto

@consento/crypto is a set of crypto primitives useful for the communication within the consento workflow.

State

Pre 1.0. This library is under heavy development. There are still updates to both the interna of this library and to namings.

Goal

libsodium is a good crypto foundation to build on but using it as-is presents various issues:

keys are all of the same type (Uint8Array) and its easy to mistake one key for another one.

This library is set out to create a good dictionary and structure on top of libsodium that enables users to clearly understand what happens where. This is achived through proper naming: for example: we distinguish verifyKey and decryptKey which would both be called pk in libsodium. This extends to the type definition which are as expressive as possible.

Users need to know both the key type and the implementation to use it which makes it prone to type errors.

In this library we have structures like Writer that keep the encryptKey needed for a encryption operation making an API like writer.encrypt('message') possible, which natively would look like crypto_box_seal(encryptKey, stringToBuffer('message')).

libsodium works with Uint8Array but users have Objects.

Any data that is processed with libsodium is binary, which gives is flexibly but not how it's used in practice. With this library comes codec support for all structures. You can specify for a read and write process to use complex data structures, even supporting custom structures if you need those. Core strategy here is to specify the types to a great detail with TypeScript. For example, the Writer has a generic information for the codec: Writer<typeof codecs.msgpack> which means you can see while coding what data the Writer can encode anything that is encodable with msgpack.

The de-/serialization of structures using libsodium can be tedious.

Everything in this library can be serialized with .toJSON() and restored with the constructor. Example: new Writer(writer.toJSON()). This allows for an easy means to preserve the data structure in a standard format. A goal for 2.0.0 is to provide protocol buffer de-/encoding to allow more efficent data structures.

Topics

Vocabulary

  • Channel - an e2e encrypted setup consisting of one Reader and one Writer
  • Writer - an object containing the keys that allow to encrypt data - it can write on that Channel - it can not read the data!
  • Reader - an object containing the keys that allow to decrypt data - it can read on that Channel - it can not write to it!
  • Verifier - an object describing an the capability to verify if a message is part of a Channel without being able to read it.
  • Connection - an e2e encrypted setup consisting of the Reader of one channel, called input and the Writer of another, called output.
  • Blob - a self-contained piece of data, like an image or pdf.
  • Handshake - the process to connect two separate processes/devices resulting in a Connection for each process.
  • SignVector - operations on a Channel may be vectored with means that there is a new sign/verify keypair for every new message. The SignVector holds the index and current sign or verify key.
  • VerifyVector - sibling to SignVector the VerifyVector allows to verify things in the order that the SignVector created it.
  • Codec - Data written by a reader or read by a writer will be transported binary (Uint8Array), a Codec specifies how an object read or written will be translated from/to binary data.

Encrypted Communication

The crypto library contains useful primitives for sending e2e encrypted messages through public channels.

const { createChannel } = require('@consento/crypto')
const { writer, reader } = createChannel()

const encrypted = writer.encrypt('hello world')
const decrypted = reader.decrypt(encrypted) === 'hello world'

You can create a new communication channel with the simple createChannel method.

const channel = createChannel()
const { reader } = channel // Can decrypt messages; _could_ encrypt messages, but these would not be signed and rejected!
const { writer } = channel // Can only encrypt messages.
const { verifier } = channel // Object that can verify messages but not de-/encrypt messages.

reader.readerKey // To backup/restore the receiver
writer.senderKey // To backup/restore the sender
reader.verifyKeyBase64 === writer.verifyKeyBase64 === verifier.verifyKeyBase64
// The lookup id is same here, the verifyKey may be used to verify the data, can also be used for the channel

writer.signKey // Allows the writer to sign messages, only privy to the writer
reader.decryptKey // Allows the reader to decrypt messages, only privy to the reader

writer.encryptKey.equals(receiver.encryptKey) // Key to encrypt messages, receiver _can_ write but not sign the message, thus it exists pro-forma

All objects created using createChannel are well de-/serializable:

const { createChannel, Reader, Writer, Verifier } = require('@consento/crypto')
const channel = createChannel()
const { reader, writer, verifier } = channel

new Channel(channel.toJSON())
new Reader(reader.toJSON())
new Writer(writer.toJSON())
new Verifier(verifier.toJSON())

Codecs

Any data sent out through Writers or Readers is encoded using mechanism, by default it will be using msgpack but you can specify any codec supported by @consento/codecs.

const { createChannel } = require('@consento/crypto')

const { writer } = createChannel({ codec: 'json' }) // 
writer.encrypt({ foo: 'hello' }) // Changes the binary format to be utf-8 encoded JSON data.

const differentCodec = new Writer({ ...writer.toJSON(), codec: 'msgpack' })
differentCodec.encrypt({ foo: 'hello' }) // Looks same but the binary data is now encoded using msgpack

Sign-Vectors

The encrypt, decrypt and verify operations can be extended using a SignVector. The SignVector allows for all operations to be in sequential order. In other words: the chunks need to be decrypted/verified in the same order as they were encrypted.

const { createChannel, createSignVectors, SignVector } = require('@consento/crypto')
const { inVector, outVector } = createSignVectors()
const { writer, reader, verifier } = createChannel()

const list = []

list.push(writer.encrypt('foo', outVector))
console.log(outVector)

list.push(writer.encrypt('bar', outVector))
console.log(outVector)

list.push(writer.encrypt('baz', outVector))
console.log(outVector)

const decryptVector = new SignVector(inVector)
for (const entry of list) {
  console.log(reader.decrypt(entry, decryptVector))
  console.log(decryptVector)
}

const verifyVector = new SignVector(inVector)
for (const entry of list) {
  try {
    verifier.verify(entry, verifyVector)
  } catch (err) {
    // not verified
  }
  console.log(verifyVector)
}

writer.encrypt(body, [signVector])

Encrypt and sign a given input with the encryptKey and signKey.

  • body - what you like to encrypt, any serializable object is possible
  • signVector - optional SignVector instance to assure order of statements. See Sign Vectors.
const encrypted = writer.encrypt('secret message')
encrypted.signature // Uint8Array
encrypted.body // Uint8Array

writer.encryptOnly(body, [signVector]), reader.encryptOnly(body, [signVector])

Only encrypt the body. This is only recommended in an environment where the signature needs to be created at a different time!

  • body - what you like to encrypt, any serializable object is possible
  • signVector - optional SignVector instance to assure order of statements. See Sign Vectors.
const encrypted = writer.encrypt('secret message')
encrypted // Uint8Array with an encrypted message

signVector.sign(message)

Signs a message in the order received.

  • message - an Uint8Array that should be signed.
const { outVector } = createSignVectors()
outVector.sign('hello world')
outVector.sign('hello world') // Different signature!

verifyVector.verify(message, signature)

Verifies that a message is encrypted with the corresponding signVector created using createSignVectors

  • message - an Uint8Array with the message for the signature
  • signature - an Uint8Array that contains the signature
const { EDecryptionError } = require('@consento/crypto')
const { inVector } = createSignVectors()
try {
  inVector.verify(message, signature)
} catch (error) {
  switch (error.code) {
    case EDecryptionError.unexpectedIndex: // Order of messages may be wrong
    case EDecryptionError.vectorIntegrity: // General vector verificaton failed
  }
}

writer.sign(data)

Signs a given data. This is only recommended in an environment where the data was encrypted at a different time!

  • data - Uint8Array for which a signature is wanted
const signature = sender.sign(sender.encryptOnly('secret message'))
signature // Uint8Array with the signature of the encrypted message

verifier.verify(signature, body, [signVector])

Using the annonymous object we can verify a given data.

  • signature - Uint8Array with the signature for the body
  • body - Uint8Array with of the encrypted data.
  • signVector - optional SignVector instance to assure order of statements. See Sign Vectors.
const encrypted = writer.encrypt('hello world')
try {
  verifier.verify(encrypted.signature, encrypted.body)
} catch (err) {
  switch (err.code) {
    case EDecryptionError.invalidSignature: // Signature doesn't match
    case EDecryptionError.unexpectedIndex: // Order of messages may be wrong, only with SignVector
    case EDecryptionError.vectorIntegrity: // General vector verificaton failed, only with SignVector
  }
}

verifier.verifyMessage(message, [signVector])

As a short-cut its also possible to just verify a message

  • message - { signature: Uint8Array, body: Uint8Array } can also be Uint8Array in combination with a signVector
  • signVector - optional SignVector instance to assure order of statements. See Sign Vectors.
try {
  verifier.verifyMessage(message)
} catch (err) {
  switch (err.code) {
    case EDecryptionError.invalidSignature: // Signature doesn't match
    case EDecryptionError.unexpectedIndex: // Order of messages may be wrong, only with SignVector
    case EDecryptionError.vectorIntegrity: // General vector verificaton failed, only with SignVector
  }
}

reader.decrypt(encrypted, [signVector])

Get the content of a once encrypted message.

  • encrypted - { signature: Uint8Array, body: Uint8Array } as created by writer.encrypt or Uint8Array created with writer.encryptOnly
  • signVector - optional SignVector instance to assure order of statements. See Sign Vectors.
const message = reader.decrypt(message:)

Establishing Connections

crypto also holds primitives for a decentralized handshake mechanism.

const { initHandshake, acceptHandshake } = require('@consento/crypto')

initHandshake is to be used by the first person - "Alice".

acceptHandshake is to be used by the second person - "Bob".

How the handshake works:

  1. Alice needs to create the initial message:

    const alice = initHandshake()
    const initMessage = alice.firstMessage
    
  2. Alice needs to listen to the channel with the id alice.receiver.id for answers that may come from Bob.

  3. Alice needs to send hand the initial message to Bob using any means. (QR Code, Email,...)

  4. Bob needs to receive the initial message

    const bob = acceptHandshake(firstMessage)
    
  5. Bob needs to listen to the channel with the id bob.receiver.id for the final message from Alice.

  6. Bob needs to send the message, encrypted to the channel with the id: bob.sender.id:

    bob.sender.encrypt(bob.acceptMessage)
    
  7. Alice has to receive the acception message and can generate the channels out of it.

    const decryptedAcceptMessage = alice.receiver.decryptMessage(acceptMessage).body
    const package = confirmHandshake(alice, decryptedAcceptMessage)
    const {
      connection: {
        sender: aliceToBobSender, // channel to send messages to Bob
        receiver: bobToAliceReceiver, // channel to receive messages from Bob
      },
      finalMessage
    } = package
    
  8. Alice has to send the final message to bob:

    aliceToBobSender.encrypt(finalMessage)
    
  9. Bob can now finalize the handshake

    const { output: bobToAliceOutput, input: aliceToBobInput } = bob.finalize(finalMessage)
    

Now Alice and Bob have each two channels: one to send data to, one to receive data from.

bobToAliceReceiver.decrypt(aliceToBobSender.encrypt('Hello Bob!')) // Hello Bob!
aliceToBobReceiver.decrypt(bobToAliceSender.encrypt('Hello Alice!')) // Hello Alice!

Encrypted Blobs

This a all-in-one API to encode, encrypt and store binary data and allow to easily encrypt it.

Only one key is necessary to find and decrypt previously encrypted data!

const { encryptBlob, isEncryptedBlob } = require('@consento/crypto')

const {
  blob, // Information about a blob: to pass around
  encrypted // Encrypted data to be stored
} = encryptBlob('Hello Secret!', 'utf8')
blob.locationKey // Key to locate an object for that secret
blob.path // Path at which to store the encrypted data, useful for file systems
blob.secretKey // Secretkey to decrypt this data
blob.size // Number of bytes of the encrypted blob (optional information)

isEncryptedBlob(blob) // To verify if a set of data is a blob

const decrypted = blob.decrypt(encrypted)

Blob information is serializable with toJSON and deserializable using the EncryptedBlob class:

const { blob } = encryptBlob('Hello Secret!', 'utf-8')
const blobJSON = blob.toJSON()
const sameBlob = new EncryptedBlob(blobJSON)

Blob storage is binary by default, if you intend to use encode other types of data use the codec option.

const { blob, encrypted } = encryptBlob({ hello: 'world' }, 'msgpack')

It is possible to restore a blob from it's secretKey alone, this may require you to pass-in a codec.

const { encryptBlob, toEncryptedBlob } = require('@consento/crypto')

const { blob } = encryptBlob('Hello Secret!')
const sameBlob = toEncryptedBlob(blob.secretKey, blob.codec.name)

License

MIT

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