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keys

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Create and store keypairs in the browser with the web crypto API.

Use indexedDB to store non-extractable keypairs in the browser. "Non-extractable" means that the browser prevents you from ever reading the private key, but the keys can still be persisted and re-used indefinitely.

Tip

Use the persist method to tell the browser not to delete from indexedDB.

Each instance of Keys has two keypairs — one for signing, and another for encrypting.

See also, the API docs generated from typescript.

Contents

Install

npm i -S @substrate-system/keys

Exports

This exposes ESM and common JS via package.json exports field.

ESM

import { EccKeys, verify } from '@substrate-system/keys/ecc'
import { RsaKeys, verify } from '@substrate-system/keys/rsa'
import { AES } from '@substrate-system/keys/aes'

Common JS

const { EccKeys, verify } = require('@substrate-system/keys/ecc')
const { RsaKeys, verify } = require('@substrate-system/keys/rsa')
const { AES } = require('@substrate-system/keys/aes')

pre-bundled JS

This package exposes minified JS files too. Copy them to a location that is accessible to your web server, then link to them in HTML.

copy

cp ./node_modules/@substrate-system/keys/dist/index.min.js ./public/keys.min.js

HTML

<script type="module" src="./keys.min.js"></script>

@substrate-system/keys

Import everything.

import * as keys from '@substrate-system/keys'

ecc

Import functions for Ed25519 signatures and X25519 encryption.

import {
  EccKeys,
  exportPublicKey,
  importPublicKey,
  verify
} from '@substrate-system/keys/ecc' 

rsa

Import RSA functions.

import {
  RsaKeys,
  encryptKeyTo,
  encryptTo,
  verify,
  publicKeyToDid,
  getPublicKeyAsUint8Array
} from '@substrate-system/keys/rsa' 

Import AES (symmetric) encryption only.

import {
  AES,
  importAesKey
} from '@substrate-system/keys/aes'

crypto

Some miscellaneous functions.

import {
  verify,
  keyTypeFromDid,
  publicKeyToDid
} from '@substrate-system/keys/crypto'

crypto.verify

The verify function exposed here will work with either RSA or Ed25519 signatures.

const eccOk = await verify({ message, did: ecc.DID, signature: eccSig })
const rsaOk = await verify({ message, did: rsa.DID, signature: rsaSig })

crypto.keyTypeFromDid

Return a string either 'rsa' or 'ed25519' given a DID.

const type = keyTypeFromDid(eccKeys.DID)
// 'ed25519'

const rsaType = keyTypeFromDid(rsaKeys.DID)
// 'rsa'

Get started

Verify a signature

This function takes either an Ed25519 key or an RSA key. This is exposed as a separate function so that you do not need to bundle all of keys just to verify something.

import { verify } from '@substrate-system/keys/crypto'

// ed25519
const isOk = await verify({ message, publicKey: ecc.DID, signature })

// RSA
const isOk = await verify({ message, publicKey: rsa.DID, signature })

ECC keys

Create a keypair

Create a new keypair, then save it in indexedDB.

ECC is now supported in all major browsers.

import { EccKeys, verify } from '@substrate-system/keys/ecc'

const keys = await EccKeys.create()

// save the keys to indexedDB
await keys.persist()

// ... sometime in the future ...
// get our keys from indexedDB
const keysAgain = await EccKeys.load()

console.assert(keys.DID === keysAgain.DID)  // true

Encrypt a Message

ECC encryption uses the ECIES (Elliptic Curve Integrated Encryption Scheme) pattern. For each encrypted message:

  1. A new ephemeral X25519 keypair is generated
  2. A new AES key is generated with the ephemeral private key and recipient's public key.
  3. The message is encrypted with the AES key.
  4. The ephemeral public key is prepended to the ciphertext

To decrypt:

  1. The recipient extracts the ephemeral public key, salt, and IV from the ciphertext
  2. The recipient's private key is combined with the ephemeral public key via ECDH to get a shared secret
  3. Recipient uses HKDF with the shared secret and salt to derive the same AES key
  4. Use the AES key and IV to decrypt the message

Note that this does not provide forward secrecy — if the recipient's long-term private key is compromised, an attacker can decrypt past messages by extracting the ephemeral public key from the ciphertext and deriving the shared secret for each message.

The good news is that this would provide forward secrecy for the sender's keys. If the sender's long-term private key is compormised, then past messages remain illegible because they were each created with a new keypair, the secret side of which has been discarded.

For true forward secrecy, you would want both parties to use ephemeral keys, like with Signal's double ratchet protocol.

Ciphertext format:

[32-byte ephemeral public key][16-byte salt][12-byte IV][ciphertext]
import { EccKeys } from '@substrate-system/keys/ecc'

const alice = await EccKeys.create()
const bob = await EccKeys.create()

// Alice encrypts a message to Bob's public key
const message = 'Hello Bob!'
const encrypted = await alice.encrypt(message, bob.publicExchangeKey)

// Bob decrypts using his private key + the ephemeral public key from the ciphertext
const decrypted = await bob.decryptAsString(encrypted)
console.log(decrypted)  // 'Hello Bob!'

// Encrypt to self (note to self)
const selfEncrypted = await alice.encrypt('Secret note')
const selfDecrypted = await alice.decryptAsString(selfEncrypted)

Multiple devices

Multiple devices need to read the same data. Generate a random AES key for the data encryption, then encrypt that AES key to each device's public key with wrap and unwrap methods.

See asymmetric docs for more about how this works.

  • Use wrap() to encrypt an AES key for a new device's public key
  • Use unwrap() on the new device to recover the AES key
  • Add devices without re-encrypting the entire dataset
import { EccKeys } from '@substrate-system/keys/ecc'
import { AES } from '@substrate-system/keys/aes'

// Device 1 has a symmetric key for encrypting data
const device1 = await EccKeys.create()
const contentKey = await AES.create({ length: 256 })

// Encrypt some data.
// (AES.encrypt automatically prepends iv to ciphertext).
const message = 'secret data for all devices'
const encrypted = await AES.encrypt(
    new TextEncoder().encode(message),
    contentKey
)

// ... device 1 needs to obtain device 2's public exchange key ...

// wrap the content key for device 2
const wrapped = await device1.wrap(contentKey, device2.publicExchangeKey)

console.log(wrapped)
// {
//   enc: 'base64-encoded-ephemeral-public-key...',
//   wrappedKey: 'base64-encoded-wrapped-content-key...'
// }

// Store encrypted data + wrapped key entries for each device


// -----------------------------------------
// device 2
// -----------------------------------------

// ... device 2 needs to obtain the wrapped key ...

const device2 = await EccKeys.create()

// Device 2 unwraps the content key
const device2ContentKey = await device2.unwrap(wrapped.enc, wrapped.wrappedKey)

// Device 2 decrypts the data with the unwrapped key
// (AES.decrypt automatically extracts iv from the encrypted data)
const decrypted = await AES.decrypt(encrypted, device2ContentKey)


console.log(new TextDecoder().decode(decrypted))
// => 'secret data for all devices'

some notes about the keys instance

keys.DID

'did:key:z13V3Sog2YaUKhdGCmgx9UZuW...'

This is the DID string for the signing key for this instance. The DID looks like this:

Ed25519 DID
did:key:zStERvoWtx7FQS432smzbGENZHjsN55X8pUZ3np8DXGhZFf3TCorijCPeJoLytwb
RSA DID
did:key:z13V3Sog2YaUKhdGCmgx9UZuW1o1ShFJYc6DvGYe7NTt689NoL2HdpC46K4PjfsUVAopaqmnySjJV8T6K9dMB2FUXhqfKYLUz9o9fA7xkgiNr25sUQq4vJPuPfP1kbSqtYXe5V2CZTUMucF2jfNMrWjHHRUZpEzPwGeZd5prsu9pxnVhPKnVxxKTJAVqQCp3CDRASeYKQmqVRmyPSrdQaYz4AoQxaBd52mNC7dEC4xXKbVw45dhQc52j5chR8YKCeaNANWh8DEZ7U8Dtb89PL5qP8817oxswQhz4e97p8EGtJDVrGbCXN4EucnpYaacRane4YPcmevs1pMYV8iqzJd8UZLWtDcUBNrCkeVTdnzXnM4Rq9sWiFwF3nYk6fxqfUZDfYyfPtxacSoGaSjo38ye

keys.getDeviceName / keys.deviceName

Return a 32 character, DNS friendly hash of the signing public key.

const name = await keys.getDeviceName()

// a promise is exposed as property `deviceName`
const name = await keys.deviceName

keys.hasPersisted

A flag indicating whether .persist has been called, meaning that these keys are saved in indexedDB.

keys.publicExchangeKey

The public encryption CryptoKey. For ECC keys, this is the X25519 exchange key. For RSA keys, this is the RSA encryption key.

keys.publicExchangeKeyAsString()

Get the public encryption key as a base64 string. For other formats, see below.

{
  async publicExchangeKeyAsString (format?:SupportedEncodings):Promise<string>
}

keys.publicWriteKey

The public signing CryptoKey. This is the Ed25519 or RSA signing key.

keys.publicWriteKeyAsString()

Get the public signing key as a string.

{
  async publicWriteKeyAsString (format?:SupportedEncodings):Promise<string>
}

Delete a keypair

Delete the keys from indexedDB.

await keys.delete()

Sign and Verify Something

.verify takes the content, the signature, and the DID for the public key used to sign. The DID is exposed as the property .DID on a Keys instance.

Note

verify is exposed as a separate function, so you don't have to include all of Keys just to verify a signature.

import { RsaKeys, verify } from '@substrate-system/keys/rsa'
// or: import { EccKeys, verify } from '@substrate-system/keys/ecc'

const keys = await RsaKeys.create()
// or: const keys = await EccKeys.create()

// sign something
const sig = await keys.signAsString('hello string')
// or string format: const sig = await keys.sign.asString('hello string')

// verify the signature
const isOk = await verify('hello string', sig, keys.DID)

encrypt something

Take the public key we are encrypting to, return encrypted content.

keys.encrypt methods

Encrypt something, return a Uint8Array.

ECC:

Note

recipient is optional. If it is omitted, then this will encrypt to its own public key, a "note to self."

async encrypt (
  content:string|Uint8Array,
  recipient?:CryptoKey|string,  // their public key
  info?:string,
  aesKey?:SymmKey|Uint8Array|string,
  keysize?:SymmKeyLength
):Promise<Uint8Array>

RSA:

async encrypt (
  content:string|Uint8Array,
  recipient?:CryptoKey|string,
  aesKey?:SymmKey|Uint8Array|string,  // For RSA, can pass in AES key
  keysize?:SymmKeyLength,
):Promise<Uint8Array>

keys.encryptAsString methods

Encrypt something, return a string.

ECC:

async encryptAsString (
  content:string|Uint8Array,
  recipient?:CryptoKey|string,
  info?:string,
  aesKey?:SymmKey|Uint8Array|string,
  keysize?:SymmKeyLength,
):Promise<string>

RSA:

async encryptAsString (
  content:string|Uint8Array,
  recipient?:CryptoKey|string,
  aesKey?:SymmKey|Uint8Array|string,
  keysize?:SymmKeyLength,
):Promise<string>
import { encryptTo } from '@substrate-system/keys/rsa'  // RSA version

// need to know the public key we are encrypting for
const publicKey = await keys.publicExchangeKeyAsString()  // Both ECC and RSA

const encrypted = await encryptTo({
  content: 'hello public key',
  publicKey
})  // => ArrayBuffer

const encrypted = await encryptTo.asString({
  content: 'hello public key',
  publicKey
})  // => <encrypted text>

decrypt something

A Keys instance has a method decrypt. The encryptedMessage argument is an ArrayBuffer, as returned from encryptTo, above.

import { EccKeys } from '@substrate-system/keys/ecc'
// or: import { RsaKeys } from '@substrate-system/keys/rsa'

const keys = await EccKeys.create()
// or: const keys = await RsaKeys.create()

// This will decrypt the message using our own public key
const decrypted = await keys.decrypt(encryptedMsg)

Examples

Create a new Keys instance

Use the factory function EccKeys.create or RsaKeys.create. The optional parameters, encryptionKeyName and writeKeyName, are added as properties to the keys instance. These are used as indexes for saving the keys in indexedDB.

ECC:

class EccKeys {
  static EXCHANGE_KEY_NAME:string = 'ecc-exchange'
  static WRITE_KEY_NAME:string = 'ecc-write'

  static async create (
    session?:boolean,  // default false
    extractable?:boolean,
    keys?:{
        exchangeKeys?:CryptoKeyPair|null,
        writeKeys?:CryptoKeyPair|null,
    }
):Promise<EccKeys>

RSA:

class RsaKeys {
  static EXCHANGE_KEY_NAME:string = 'rsa-exchange'
  static WRITE_KEY_NAME:string = 'rsa-write'

  static async create (
    session?:boolean,  // defaut false
    extractable?:boolean,
    keys?:{
        exchangeKeys?:CryptoKeyPair|null,
        writeKeys?:CryptoKeyPair|null,
    }
  ):Promise<RsaKeys> {
}

Parameters

  • session (optional, boolean): If true, keys are created in memory only and won't be saved to indexedDB even if persist() is called.
  • extractable (optional, boolean): If true, creates extractable keys that can be exported/read. Defaults to false for security.

Warning

Set extractable: true only when you need to export private keys. Non-extractable keys (default) are better for security.

.create() example

Use the factory function b/c async.

import { EccKeys } from '@substrate-system/keys/ecc'
// or: import { RsaKeys } from '@substrate-system/keys/rsa'

// Create non-extractable keys (recommended)
const keys = await EccKeys.create()

// Create extractable keys (only when export is needed)
const extractableKeys = await EccKeys.create(false, true)

// Create session-only, extractable keys
const sessionKeys = await EccKeys.create(true, true)

// Session-only keys are not persisted.

Get a hash of the DID

Get a 32-character, DNS-friendly string of the hash of the given DID. Available as static or instance method. If called as an instance method, this will use the DID assigned to the given Keys instance.

The static method requires a DID string to be passed in.

Static deviceName method

class EccKeys {  // or RsaKeys
  static async deviceName (did:DID):Promise<string>
}

Instance getdeviceName method

If used as an instance method, this will use the DID assigned to the instance.

class EccKeys {  // or RsaKeys
  async getDeviceName ():Promise<string>
}

Persist the keys

Save the keys to indexedDB. This depends on the values of the static class properties EXCHANGE_KEY_NAME and WRITE_KEY_NAME. Set them if you want to change the indexes under which the keys are saved to indexedDB.

Defaults for indexedDB:

  • ECC: 'ecc-exchange' and 'ecc-write'
  • RSA: 'rsa-exchange-key' and 'rsa-write-key'

.persist

class EccKeys {  // or RsaKeys
  async persist ():Promise<void>
}

.persist example

import { EccKeys } from '@substrate-system/keys/ecc'

const keys = await EccKeys.create()
EccKeys.EXCHANGE_KEY_NAME = 'encryption-key-custom-name'
EccKeys.WRITE_KEY_NAME = 'signing-key-custom-name'
await keys.persist()

Restore from indexedDB

Create a Keys instance from data saved to indexedDB. Pass in different indexedDB key names for the keys if you need to.

static .load

class EccKeys {  // or RsaKeys
    static async load (opts?:{
      encryptionKeyName?:string,
      writeKeyName?:string,
      session?:boolean,
      extractable?:boolean,
    }):Promise<EccKeys>
}

Parameters

  • encryptionKeyName (optional, string): Custom name for the encryption key in indexedDB
  • writeKeyName (optional, string): Custom name for the signing key in indexedDB
  • session (optional, boolean): If true, creates session-only keys if no keys exist in indexedDB
  • extractable (optional, boolean): If true and keys don't exist in indexedDB, new keys will be created as extractable. Defaults to false.

example

import { EccKeys } from '@substrate-system/keys/ecc'
// or: import { RsaKeys } from '@substrate-system/keys/rsa'

// Load existing keys from indexedDB, or create new non-extractable ones
const newKeys = await EccKeys.load()

// Load with custom options
const customKeys = await EccKeys.load({
  encryptionKeyName: 'my-custom-encryption-key',
  writeKeyName: 'my-custom-signing-key',
  extractable: true  // If keys don't exist, create them as extractable
})

Sign something

Create a new signature for the given input.

ECC:

async sign (msg:Msg, _charsize?:CharSize):Promise<Uint8Array>

RSA:

async sign (
  msg:Msg,
  charsize:CharSize = DEFAULT_CHAR_SIZE
):Promise<Uint8Array>

example

const sig = await keys.sign('hello signatures')

Get a signature as a string

keys.signAsString(msg)

Sign a message and return the signature as a base64 encoded string.

{
  async signAsString (msg:string, charsize?:CharSize):Promise<string>
}
const sig = await keys.signAsString('hello string')
// => ubW9PIjb360v...

Backward compatibility: keys.sign.asString(msg)

For backward compatibility, the .asString method is still available:

const sig = await keys.sign.asString('hello string')
// => ubW9PIjb360v...

Verify a signature

Check if a given signature is valid. This is exposed as a stateless function so that it can be used independently from any keypairs. You need to pass in the data that was signed, the signature, and the DID string of the public key used to create the signature.

This works the same for either RSA or ECC keys.

async function verify (
    msg:string|Uint8Array,
    sig:string|Uint8Array,
    signingDid:DID
):Promise<boolean>

RSA verification uses RSA-PSS with SHA-256:

import { verify } from '@substrate-system/keys/rsa'

const isOk = await verify('hello string', sig, keys.DID)

ECC verification uses Ed25519:

import { verify } from '@substrate-system/keys/ecc'

const isOk = await verify('hello string', sig, keys.DID)

Encrypt a key

Use asymmetric (RSA) encryption to encrypt an AES key to the given public key.

async function encryptKeyTo ({ key, publicKey }:{
    key:string|Uint8Array|CryptoKey;
    publicKey:CryptoKey|Uint8Array|string;
}, format?:'uint8array'|'arraybuffer'):Promise<Uint8Array|ArrayBuffer>

example

import { encryptKeyTo } from '@substrate-system/keys/rsa'

// pass in a CryptoKey
const encrypted = await encryptKeyTo({
    key: myAesKey,
    publicKey: keys.publicExchangeKey
})

// pass in a base64 string
const encryptedTwo = await encryptKeyTo({
  key: aesKey,
  publicKey: await keys.publicExchangeKeyAsString()
})  // => Uint8Array

encrypt a key, return a string

Encrypt the given key to the public key, and return the result as a base64 string.

!NOTE This is only relevant for RSA keys

import { encryptKeyTo } from '@substrate-system/keys/rsa'

encryptKeyTo.asString = async function ({ key, publicKey }:{
    key:string|Uint8Array|CryptoKey;
    publicKey:CryptoKey|string|Uint8Array;
}, format?:SupportedEncodings):Promise<string> {

format

encryptKeyTo.asString takes an optional second argument for the format of the returned string. Format is anything supported by uint8arrays. By default, if omitted, it is base64.

Asymmetrically encrypt some arbitrary data

Encrypt the given message to the given public key. If an AES key is not provided, one will be created. Use the AES key to encrypt the given content, then encrypt the AES key to the given public key.

!NOTE This is only relevant for RSA keys. If using ECC keys, a symmetric key is automatically generated via diffie-hellman.

The return value is an ArrayBuffer containing the encrypted AES key + the iv + the encrypted content if using RSA. It is salt + iv + cipher text if using ECC.

To decrypt, pass the returned value to keys.decrypt, where keys is an instance with the corresponding private key.

async function encryptTo (
    opts:{
        content:string|Uint8Array;
        publicKey:CryptoKey|string;
    },
    aesKey?:SymmKey|Uint8Array|string,
):Promise<ArrayBuffer>

example

import { encryptTo } from '@substrate-system/keys/rsa'

const encrypted = await encryptTo({
    content: 'hello encryption',
    publicKey: keys.publicExchangeKey
})

// => ArrayBuffer

Asymmetrically encrypt a string, return a new string

Encrypt the given string, and return a new string that is the (encrypted) AES key concatenated with the iv and cipher text. The corresponding method keys.decryptAsString will know how to parse and decrypt the resulting text.

Use the functions encryptTo.asString and keys.decryptAsString.

keys.decryptAsString

ECC:

async decryptAsString (
  msg:string|Uint8Array|ArrayBuffer,
  publicKey?:CryptoKey|string,
  aesAlgorithm?:string,
  info?:string,
):Promise<string>

RSA:

async decryptAsString (
  msg:string|Uint8Array|ArrayBuffer,
  keysize?:CryptoKey|string|SymmKeyLength,
  _aesAlgorithm?:string,
):Promise<string>
example
import { RsaKeys, encryptTo } from '@substrate-system/keys/rsa'  // RSA example
// or: import { EccKeys } from '@substrate-system/keys/ecc'

const keys = await RsaKeys.create()
// or: const keys = await EccKeys.create()
const pubKey = await keys.publicExchangeKeyAsString()  // Both ECC and RSA
const msg = { type: 'test', content: 'hello' }
const cipherText = await encryptTo.asString({
    content: JSON.stringify(msg),
    // pass in a string public key or crypto key or Uint8Array
    publicKey: pubKey
})  // => string

const text = await keys.decryptAsString(cipherText)
const data = JSON.parse(text)
// => { type: 'test', content: 'hello' }

Decrypt a message

ECC:

async decrypt (
  msg:string|Uint8Array|ArrayBuffer,
  publicKey?:CryptoKey|string,
  aesAlgorithm?:string,
  info?:string,
):Promise<ArrayBuffer>

!NOTE ECC keys will use our own public key if it is not passed in.

RSA:

async decrypt (
  msg:string|Uint8Array|ArrayBuffer,
  keysize?:CryptoKey|string|SymmKeyLength,
  _aesAlgorithm?:string,
):Promise<Uint8Array>
const decrypted = await keys.decrypt(encrypted)
// => ArrayBuffer (ECC) or Uint8Array (RSA)

In memory only

Create a keypair, but do not save it in indexedDB, even if you call persist. Pass true as the session parameter to .create or pass { session: true } to .load.

import { EccKeys } from '@substrate-system/keys/ecc'
// or: import { RsaKeys } from '@substrate-system/keys/rsa'

const keys = await EccKeys.create(true)
// or: const keys = await RsaKeys.create(true)

// or pass it to `.load`
const keysTwo = await EccKeys.load({ session: true })
// or: const keysTwo = await RsaKeys.load({ session: true })

AES

Expose several AES functions, use nice defaults.

import { AES } from '@substrate-system/keys/aes'

const key = await AES.create(/* ... optional arguments ... */)

create

Create a new AES key. By default uses 256 bits & GCM algorithm.

import {
  DEFAULT_SYMM_ALGORITHM,
  DEFAULT_SYMM_LENGTH
} from '@substrate-system/keys/constants'

function create (opts:{ alg:string, length:number } = {
    alg: DEFAULT_SYMM_ALGORITHM,  // AES-GCM
    length: DEFAULT_SYMM_LENGTH  // 256
}):Promise<CryptoKey>
import { AES } from '@substrate-system/keys/aes'
const aesKey = await AES.create()

export

Get the AES key as a Uint8Array.

export const AES = {
  async export (key:CryptoKey):Promise<Uint8Array>
}

aes.export example

import { AES } from '@substrate-system/keys/aes'

const exported = await AES.export(myAesKey)

export.asString

Get the key as a string, base64 encoded by default.

async function asString (
  key:CryptoKey,
  format?:SupportedEncoding
):Promise<string>

export.asString example

import { AES } from '@substrate-system/keys/aes'

const exported = await AES.export.asString(myAesKey)
// => QlfjZKzzgtNMVC4fPY7S537r/PFstifTyYqcsbsCjHQ=

const base32 = await AES.export.asString(myAesKey, 'base32')
// => ijl6gzfm6obngtcufypt3dws457ox7hrns3cpu6jrkoldoycrr2a

AES.encrypt

Take a Uint8Array, return an encrypted Uint8Array.

async function encrypt (
  data:Uint8Array,
  cryptoKey:CryptoKey|Uint8Array,
  iv?:Uint8Array
):Promise<Uint8Array>
import { AES } from '@substrate-system/keys/aes'
import { fromString } from 'uint8arrays'

const encryptedText = await AES.encrypt(fromString('hello AES'), aesKey)

AES.decrypt

async function decrypt (
  encryptedData:Uint8Array|string,
  cryptoKey:CryptoKey|Uint8Array|ArrayBuffer,
  iv?:Uint8Array
):Promise<Uint8Array>
import { toString } from 'uint8arrays'
import { AES } from '@substrate-system/keys/aes'

const decryped = await AES.decrypt(encryptedText, aesKey)
const decryptedText = toString(decrypted)
// => 'hello AES'

See also

About

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