The sodium R package provides bindings to libsodium: a modern, easy-to-use software library for encryption, decryption, signatures, password hashing and more.
The goal of Sodium is to provide the core operations needed to build higher-level cryptographic tools. It is not intended for implementing standardized protocols such as TLS, SSH or GPG. Sodium only supports a limited set of state-of-the-art elliptic curve methods, resulting in a simple but very powerful tool-kit for building secure applications.
Using Sodium
All Sodium functions operate on binary data, called ‘raw’ vectors in R. Use charToRaw and rawToChar to convert between strings and raw vectors. Alternatively hex2bin and bin2hex can convert between binary data to strings in hex notation:
test <- hash(charToRaw("test 123"))
str <- bin2hex(test)
print(str)
[1] "e8b785b02e702c0b7edc9683130db36c91e0241ba0c489ff1e20cbb4fa3920f9"
hex2bin(str)
[1] e8 b7 85 b0 2e 70 2c 0b 7e dc 96 83 13 0d b3 6c 91 e0 24 1b a0 c4 89
[24] ff 1e 20 cb b4 fa 39 20 f9
Random data generator
The random() function generates n bytes of unpredictable data, suitable for creating secret keys.
secret <- random(8)
print(secret)
[1] 90 70 7a fd 1d 39 bc 75
Implementation is platform specific, see the docs for details.
Hash functions
Sodium has several hash functions including hash(), shorthash(), sha256(), sha512 and scrypt(). The generic hash() is usually recommended. It uses blake2b with a configurable size between 16 bytes (128bit) and 64 bytes (512bit).
# Generate keys from passphrase
passphrase <- charToRaw("This is super secret")
hash(passphrase)
[1] 98 5c 9b b6 f6 92 d5 26 10 80 99 25 3e a5 a6 66 67 13 fd 88 10 b6 12
[24] 74 86 c8 e9 5c 44 07 45 f5
hash(passphrase, size = 16)
[1] eb 6c df 04 18 40 16 28 c1 b0 2e 76 f3 e6 bd 89
hash(passphrase, size = 64)
[1] d0 89 68 30 26 1d 1b 85 76 dc ad 20 c9 58 0a fb b1 d0 62 ba 10 d6 80
[24] f6 cb c6 ae 2d 42 57 ee a0 65 fd b0 e8 90 02 ae b3 e0 4f 88 df ba ea
[47] 26 bb 47 3f 29 5a a4 06 cd b8 05 78 83 31 66 dc 7b 24
The shorthash() function is a special 8 byte (64 bit) hash based on SipHash-2-4. The output of this function is only 64 bits (8 bytes). It is useful for in e.g. Hash tables, but it should not be considered collision-resistant.
Secret key encryption
Symmetric encryption uses the same secret key for both encryption and decryption. It is mainly useful for encrypting local data, or as a building block for more complex methods.
Most encryption methods require a nonce: a piece of non-secret unique data that is used to randomize the cipher. This allows for safely using the same key for encrypting multiple messages. The nonce should be stored or shared along with the ciphertext.
key <- hash(charToRaw("This is a secret passphrase"))
msg <- serialize(iris, NULL)
# Encrypt with a random nonce
nonce <- random(24)
cipher <- data_encrypt(msg, key, nonce)
# Decrypt with same key and nonce
orig <- data_decrypt(cipher, key, nonce)
identical(iris, unserialize(orig))
[1] TRUE
Because the secret has to be known by all parties, symmetric encryption by itself is often impractical for communication with third parties. For this we need asymmetric (public key) methods.
Secret key authentication
Secret key authentication is called tagging in Sodium. A tag is basically a hash of the data together with a secret key.
key <- hash(charToRaw("This is a secret passphrase"))
msg <- serialize(iris, NULL)
mytag <- data_tag(msg, key)
To verify the integrity of the data at a later point in time, simply re-calculate the tag with the same key:
stopifnot(identical(mytag, data_tag(msg, key)))
The secret key protects against forgery of the data+tag by an intermediate party, as would be possible with a regular checksum.
Public key encryption
Where symmetric methods use the same secret key for encryption and decryption, asymmetric methods use a key-pair consisting of a public key and private key. The private key is secret and only known by its owner. The public key on the other hand can be shared with anyone. Public keys are often published on the user’s website or posted in public directories or keyservers.
key <- keygen()
pub <- pubkey(key)
In public key encryption, data encrypted with a public key can only be decrypted using the corresponding private key. This allows anyone to send somebody a secure message by encrypting it with the receivers public key. The encrypted message will only be readable by the owner of the corresponding private key.
# Encrypt message with pubkey
msg <- serialize(iris, NULL)
ciphertext <- simple_encrypt(msg, pub)
# Decrypt message with private key
out <- simple_decrypt(ciphertext, key)
stopifnot(identical(out, msg))
Public key authentication (signatures)
Public key authentication works the other way around. First, the owner of the private key creates a ‘signature’ (an authenticated checksum) for a message in a way that allows anyone who knows his/her public key to verify the integrity of the message and identity of the sender.
Currently sodium requires a different type of key-pair for signatures (ed25519) than for encryption (curve25519).
# Generate signature keypair
key <- sig_keygen()
pubkey <- sig_pubkey(key)
# Create signature with private key
msg <- serialize(iris, NULL)
sig <- sig_sign(msg, key)
print(sig)
[1] 75 b0 62 9b 52 e0 2a 00 21 f2 f1 d8 61 09 a7 88 25 82 5c 4a a6 c7 c5
[24] 4e 8f 0c c6 ff 6d 57 26 71 94 b7 6a 15 c9 a3 b6 c9 d6 80 6a 04 93 7a
[47] 7e 81 b6 95 b7 01 20 20 77 f0 77 ea d4 7f 52 f2 67 05
# Verify a signature from public key
sig_verify(msg, sig, pubkey)
[1] TRUE
Signatures are useful when the message itself is not confidential but integrity is important. A common use is for software repositories where to include an index file with checksums for all packages, signed by the repository maintainer. This allows client package managers to verify that the binaries were not manipulated by intermediate parties during the distribution process.
Public key authenticated encryption
Authenticated encryption implements best practices for secure messaging. It requires that both sender and receiver have a keypair and know each other’s public key. Each message gets authenticated with the key of the sender and encrypted with the key of the receiver.
# Bob's keypair:
bob_key <- keygen()
bob_pubkey <- pubkey(bob_key)
# Alice's keypair:
alice_key <- keygen()
alice_pubkey <- pubkey(alice_key)
# Bob sends encrypted message for Alice:
msg <- charToRaw("TTIP is evil")
ciphertext <- auth_encrypt(msg, bob_key, alice_pubkey)
# Alice verifies and decrypts with her key
out <- auth_decrypt(ciphertext, alice_key, bob_pubkey)
stopifnot(identical(out, msg))
# Alice sends encrypted message for Bob
msg <- charToRaw("Let's protest")
ciphertext <- auth_encrypt(msg, alice_key, bob_pubkey)
# Bob verifies and decrypts with his key
out <- auth_decrypt(ciphertext, bob_key, alice_pubkey)
stopifnot(identical(out, msg))
Note that even though public keys are not confidential, you should not exchange them over the same insecure channel you are trying to protect. If the connection is being tampered with, the attacker could simply replace the key with another one to hijack the interaction.
sodium/inst/doc/crypto101.html 0000644 0001762 0000144 00002576311 13063263647 015755 0 ustar ligges users
This page attempts to give a very basic conceptual introduction to cryptographic methods. Before we start the usual disclaimer:
I am not a cryptographer. This document is only for educational purposes. Crypto is hard, you should never trust your home-grown implementation. Unless you’re a cryptographer you will probably overlook some crucial details. Developers should only use the high-level functions that have been implemented by an actual cryptographer.
Now that we got this is out of the way, let’s start hacking :)
The XOR operator
The bitwise XOR operator outputs true only when both inputs differ (one is true, the other is false). It is sometimes called an invertor because the output of a bit in x gets inverted if and only if the corresponding bit in y is true:
# XOR two (8bit) bytes 'x' and 'y'
x <- as.raw(0x7a)
y <- as.raw(0xe4)
z <- base::xor(x, y)
dput(z)
as.raw(0x9e)
# Show the bits in each byte
cbind(x = rawToBits(x), y = rawToBits(y), z = rawToBits(z))
x y z
[1,] 00 00 00
[2,] 01 00 01
[3,] 00 01 01
[4,] 01 00 01
[5,] 01 00 01
[6,] 01 01 00
[7,] 01 01 00
[8,] 00 01 01
In cryptography we xor a message x with secret random data y. Because each bit in y is randomly true with probability 0.5, the xor output is completely random and uncorrelated to x. This is called perfect secrecy. Only if we know y we can decipher the message x.
# Encrypt message using random one-time-pad
msg <- charToRaw("TTIP is evil")
one_time_pad <- random(length(msg))
ciphertext <- base::xor(msg, one_time_pad)
# It's really encrypted
rawToChar(ciphertext)
[1] "\xe9\x8c8\u009fd\xfd\x93\xf1\xed/%"
# Decrypt with same pad
rawToChar(base::xor(ciphertext, one_time_pad))
[1] "TTIP is evil"
This method is perfectly secure and forms the basis for most cryptograhpic methods. However the challenge is generating and communicating unique pseudo-random y data every time we want to encrypt something. One-time-pads as in the example are not very practical for large messages. Also we should never re-use a one-time-pad y for encrypting multiple messages, as this compromises the secrecy.
Stream ciphers
The solution to this problem are stream ciphers. A stream cipher generates a unique stream of pseudo-random data based on a secret key and a unique nonce. For a given set of parameters the stream cipher always generates the same stream of data. Sodium implements a few popular stream ciphers:
password <- "My secret passphrase"
key <- hash(charToRaw(password))
nonce <- random(8)
chacha20(size = 20, key, nonce)
[1] bb 96 2f 70 96 7d bd 2d ee 20 b5 e6 61 50 59 7b e7 be d1 9f
Each stream requires a key and a nonce. The key forms the shared secret and should only be known to trusted parties. The nonce is not secret and is stored or sent along with the ciphertext. The purpose of the nonce is to make a random stream unique to protect gainst re-use attacks. This way you can re-use a your key to encrypt multiple messages, as long as you never re-use the same nonce.
salsa20(size = 20, key, nonce)
[1] 56 47 ff d1 96 14 3a f2 f2 70 30 fe ba 8a 05 1e 74 2a 4d be
Over the years cryptographers have come up with many more variants. Many stream ciphers are based on a block cipher such as AES: a keyed permutation of fixed length amount of data. The block ciphers get chained in a particular mode of operation which repeatedly applies the cipher’s single-block operation to securely transform amounts of data larger than a block.
We are not going to discuss implementation details, but you could probably come up with something yourself. For example you could use a hash function such sha256 as the block cipher and append counter which is incremented for each block (this is called CTR mode).
# Illustrative example.
sha256_ctr <- function(size, key, nonce){
n <- ceiling(size/32)
output <- raw()
for(i in 1:n){
counter <- packBits(intToBits(i))
block <- sha256(c(key, nonce, counter))
output <- c(output, block)
}
return(output[1:size])
}
This allows us to generate an arbitrary length stream from a single secret key:
password <- "My secret passphrase"
key <- hash(charToRaw(password))
nonce <- random(8)
sha256_ctr(50, key, nonce)
[1] e3 29 96 fb b5 bd 15 d7 55 df d7 b3 1e 12 d1 5c 0b 74 86 4a 5d 85 b3
[24] bf aa 62 bb 6e 0b d3 bf ab 05 a2 31 9f a6 3a fd 83 1d 26 9f 7f 35 8d
[47] eb ec eb c3
In practice, you should never write your own ciphers. A lot of research goes into studying the properties of block ciphers under various modes of operation. In the remainder we just use the standard Sodium ciphers: chacha20, salsa20 or xsalsa20.
Symmetric encryption
Symmetric encryption means that the same secret key is used for both encryption and decryption. All that is needed to implement symmetric encryption is xor and a stream cipher. For example to encrypt an arbitrary length message using password:
# Encrypt 'message' using 'password'
myfile <- file.path(R.home(), "COPYING")
message <- readBin(myfile, raw(), file.info(myfile)$size)
passwd <- charToRaw("My secret passphrase")
A hash function converts the password to a key of suitable size for the stream cipher, which we use to generate a psuedo random stream of equal length to the message:
# Basic secret key encryption
key <- hash(passwd)
nonce8 <- random(8)
stream <- chacha20(length(message), key, nonce8)
ciphertext <- base::xor(stream, message)
Now the ciphertext is an encrypted version of the message. Only those that know the key and the nonce can re-generate the same keystream in order to xor the ciphertext back into the original message.
# Decrypt with the same key
key <- hash(charToRaw("My secret passphrase"))
stream <- chacha20(length(ciphertext), key, nonce8)
out <- base::xor(ciphertext, stream)
# Print part of the message
cat(substring(rawToChar(out), 1, 120))
GNU GENERAL PUBLIC LICENSE
Version 2, June 1991
Copyright (C) 1989, 1991 Free Software Foundation, Inc.
The Sodium functions data_encrypt and data_decrypt provide a more elaborate implementation of the above. This is what you should use in practice for secret key encryption.
Symmetric encryption can be used for e.g. encrypting local data. However because the same secret is used for both encryption and decryption, it is impractical for communication with other parties. For exchanging secure messages we need public key encryption.
Public-key encryption and Diffie-Hellman
Rather than using a single secret-key, assymetric (public key) encryption requires a keypair, consisting of a public key for encryption and a private-key for decryption. Data that is encrypted using a given public key can only be decrypted using the corresponding private key.
The public key is not confidential and can be shared on e.g. a website or keyserver. This allows anyone to send somebody a secure message by encrypting it with the receivers public key. The encrypted message will only be readable by the owner of the corresponding private key.
# Create keypair
key <- keygen()
pub <- pubkey(key)
# Encrypt message for receiver using his/her public key
msg <- serialize(iris, NULL)
ciphertext <- simple_encrypt(msg, pub)
# Receiver decrypts with his/her private key
out <- simple_decrypt(ciphertext, key)
identical(msg, out)
[1] TRUE
How does this work? Public key encryption makes use of Diffie-Hellman (D-H): a method which allows two parties that have no prior knowledge of each other to jointly establish a shared secret key over an insecure channel. In the most simple case, both parties generate a temporary keypair and exchange their public key over the insecure channel. Then both parties use the D-H function to calculcate the (same) shared secret key by combining their own private key with the other person’s public key:
# Bob generates keypair
bob_key <- keygen()
bob_pubkey <- pubkey(bob_key)
# Alice generates keypair
alice_key <- keygen()
alice_pubkey <- pubkey(alice_key)
# After Bob and Alice exchange pubkey they can both derive the secret
alice_secret <- diffie_hellman(alice_key, bob_pubkey)
bob_secret <- diffie_hellman(bob_key, alice_pubkey)
identical(alice_secret, bob_secret)
[1] TRUE
Once the shared secret has been established, both parties can discard their temporary public/private key and use the shared secret to start encrypting communications with symmetric encryption as discussed earlier. Because the shared secret cannot be calculated using only the public keys, the process is safe from eavesdroppers.
The classical Diffie-Hellman method is based on the discrete logarithm problem with large prime numbers. Sodium uses curve25519, a state-of-the-art D-H function by Daniel Bernsteinan designed for use with the elliptic curve Diffie–Hellman (ECDH) key agreement scheme.
sodium/inst/doc/intro.R 0000644 0001762 0000144 00000005304 13063263647 014566 0 ustar ligges users ## ---- echo = FALSE, message = FALSE--------------------------------------
knitr::opts_chunk$set(comment = "")
library(sodium)
## ------------------------------------------------------------------------
test <- hash(charToRaw("test 123"))
str <- bin2hex(test)
print(str)
hex2bin(str)
## ------------------------------------------------------------------------
secret <- random(8)
print(secret)
## ------------------------------------------------------------------------
# Generate keys from passphrase
passphrase <- charToRaw("This is super secret")
hash(passphrase)
hash(passphrase, size = 16)
hash(passphrase, size = 64)
## ------------------------------------------------------------------------
key <- hash(charToRaw("This is a secret passphrase"))
msg <- serialize(iris, NULL)
# Encrypt with a random nonce
nonce <- random(24)
cipher <- data_encrypt(msg, key, nonce)
# Decrypt with same key and nonce
orig <- data_decrypt(cipher, key, nonce)
identical(iris, unserialize(orig))
## ------------------------------------------------------------------------
key <- hash(charToRaw("This is a secret passphrase"))
msg <- serialize(iris, NULL)
mytag <- data_tag(msg, key)
## ------------------------------------------------------------------------
stopifnot(identical(mytag, data_tag(msg, key)))
## ------------------------------------------------------------------------
key <- keygen()
pub <- pubkey(key)
## ------------------------------------------------------------------------
# Encrypt message with pubkey
msg <- serialize(iris, NULL)
ciphertext <- simple_encrypt(msg, pub)
# Decrypt message with private key
out <- simple_decrypt(ciphertext, key)
stopifnot(identical(out, msg))
## ------------------------------------------------------------------------
# Generate signature keypair
key <- sig_keygen()
pubkey <- sig_pubkey(key)
# Create signature with private key
msg <- serialize(iris, NULL)
sig <- sig_sign(msg, key)
print(sig)
# Verify a signature from public key
sig_verify(msg, sig, pubkey)
## ------------------------------------------------------------------------
# Bob's keypair:
bob_key <- keygen()
bob_pubkey <- pubkey(bob_key)
# Alice's keypair:
alice_key <- keygen()
alice_pubkey <- pubkey(alice_key)
# Bob sends encrypted message for Alice:
msg <- charToRaw("TTIP is evil")
ciphertext <- auth_encrypt(msg, bob_key, alice_pubkey)
# Alice verifies and decrypts with her key
out <- auth_decrypt(ciphertext, alice_key, bob_pubkey)
stopifnot(identical(out, msg))
# Alice sends encrypted message for Bob
msg <- charToRaw("Let's protest")
ciphertext <- auth_encrypt(msg, alice_key, bob_pubkey)
# Bob verifies and decrypts with his key
out <- auth_decrypt(ciphertext, bob_key, alice_pubkey)
stopifnot(identical(out, msg))
sodium/inst/doc/crypto101.rmd 0000644 0001762 0000144 00000022526 13063263647 015563 0 ustar ligges users ---
title: "How does cryptography work?"
output: html_document
date: "`r Sys.Date()`"
vignette: >
%\VignetteIndexEntry{How does cryptography work}
%\VignetteEngine{knitr::rmarkdown}
\usepackage[utf8]{inputenc}
---
```{r, echo = FALSE, message = FALSE}
knitr::opts_chunk$set(comment = "")
library(sodium)
# hack for printable bits
random <- function(n = 1){
if(n != nchar("TTIP is evil"))
return(sodium::random(n))
repeat {
x <- sodium::random(n)
y <- base::xor(charToRaw("TTIP is evil"), x)
if(all(c(x,y) != 0)) return(x)
}
}
```
This page attempts to give a very basic conceptual introduction to cryptographic methods. Before we start the usual disclaimer:
___I am not a cryptographer. This document is only for educational purposes. Crypto is hard, you should never trust your home-grown implementation. Unless you're a cryptographer you will probably overlook some crucial details. Developers should only use the high-level functions that have been implemented by an actual cryptographer.___
Now that we got this is out of the way, let's start hacking :)
### The XOR operator
The bitwise [XOR operator](https://en.wikipedia.org/wiki/Exclusive_or#Truth_table) outputs `true` only when both inputs differ (one is `true`, the other is `false`). It is sometimes called an *invertor* because the output of a bit in `x` gets inverted if and only if the corresponding bit in `y` is true:
```{r}
# XOR two (8bit) bytes 'x' and 'y'
x <- as.raw(0x7a)
y <- as.raw(0xe4)
z <- base::xor(x, y)
dput(z)
# Show the bits in each byte
cbind(x = rawToBits(x), y = rawToBits(y), z = rawToBits(z))
```
In cryptography we `xor` a message `x` with secret random data `y`. Because each bit in `y` is randomly `true` with probability 0.5, the `xor` output is completely random and uncorrelated to `x`. This is called *perfect secrecy*. Only if we know `y` we can decipher the message `x`.
```{r}
# Encrypt message using random one-time-pad
msg <- charToRaw("TTIP is evil")
one_time_pad <- random(length(msg))
ciphertext <- base::xor(msg, one_time_pad)
# It's really encrypted
rawToChar(ciphertext)
# Decrypt with same pad
rawToChar(base::xor(ciphertext, one_time_pad))
```
This method is perfectly secure and forms the basis for most cryptograhpic methods. However the challenge is generating and communicating unique pseudo-random `y` data every time we want to encrypt something. One-time-pads as in the example are not very practical for large messages. Also we should never re-use a one-time-pad `y` for encrypting multiple messages, as this compromises the secrecy.
### Stream ciphers
The solution to this problem are stream ciphers. A *stream cipher* generates a unique stream of pseudo-random data based on a secret `key` and a unique `nonce`. For a given set of parameters the stream cipher always generates the same stream of data. Sodium implements a few popular stream ciphers:
```{r}
password <- "My secret passphrase"
key <- hash(charToRaw(password))
nonce <- random(8)
chacha20(size = 20, key, nonce)
```
Each stream requires a `key` and a `nonce`. The key forms the shared secret and should only be known to trusted parties. The `nonce` is not secret and is stored or sent along with the ciphertext. The purpose of the `nonce` is to make a random stream unique to protect gainst re-use attacks. This way you can re-use a your key to encrypt multiple messages, as long as you never re-use the same nonce.
```{r}
salsa20(size = 20, key, nonce)
```
Over the years cryptographers have come up with many more variants. Many stream ciphers are based on a block cipher such as [AES](https://en.wikipedia.org/wiki/Advanced_Encryption_Standard): a keyed permutation of fixed length amount of data. The block ciphers get chained in a particular [mode of operation](https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation) which repeatedly applies the cipher's single-block operation to securely transform amounts of data larger than a block.
We are not going to discuss implementation details, but you could probably come up with something yourself. For example you could use a hash function such `sha256` as the block cipher and append counter which is incremented for each block (this is called CTR mode).
```{r}
# Illustrative example.
sha256_ctr <- function(size, key, nonce){
n <- ceiling(size/32)
output <- raw()
for(i in 1:n){
counter <- packBits(intToBits(i))
block <- sha256(c(key, nonce, counter))
output <- c(output, block)
}
return(output[1:size])
}
```
This allows us to generate an arbitrary length stream from a single secret key:
```{r}
password <- "My secret passphrase"
key <- hash(charToRaw(password))
nonce <- random(8)
sha256_ctr(50, key, nonce)
```
In practice, you should never write your own ciphers. A lot of [research](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.58.1811&rep=rep1&type=pdf) goes into studying the properties of block ciphers under various modes of operation. In the remainder we just use the standard Sodium ciphers: [`chacha20`](https://download.libsodium.org/libsodium/content/advanced/chacha20.html), [`salsa20`](https://download.libsodium.org/libsodium/content/advanced/salsa20.html) or [`xsalsa20`](https://download.libsodium.org/libsodium/content/advanced/xsalsa20.html).
### Symmetric encryption
Symmetric encryption means that the same secret key is used for both encryption and decryption. All that is needed to implement symmetric encryption is `xor` and a stream cipher. For example to encrypt an arbitrary length `message` using `password`:
```{r}
# Encrypt 'message' using 'password'
myfile <- file.path(R.home(), "COPYING")
message <- readBin(myfile, raw(), file.info(myfile)$size)
passwd <- charToRaw("My secret passphrase")
```
A hash function converts the password to a key of suitable size for the stream cipher, which we use to generate a psuedo random stream of equal length to the message:
```{r}
# Basic secret key encryption
key <- hash(passwd)
nonce8 <- random(8)
stream <- chacha20(length(message), key, nonce8)
ciphertext <- base::xor(stream, message)
```
Now the `ciphertext` is an encrypted version of the message. Only those that know the `key` and the `nonce` can re-generate the same keystream in order to `xor` the ciphertext back into the original message.
```{r}
# Decrypt with the same key
key <- hash(charToRaw("My secret passphrase"))
stream <- chacha20(length(ciphertext), key, nonce8)
out <- base::xor(ciphertext, stream)
# Print part of the message
cat(substring(rawToChar(out), 1, 120))
```
The Sodium functions `data_encrypt` and `data_decrypt` provide a more elaborate implementation of the above. This is what you should use in practice for secret key encryption.
Symmetric encryption can be used for e.g. encrypting local data. However because the same secret is used for both encryption and decryption, it is impractical for communication with other parties. For exchanging secure messages we need public key encryption.
### Public-key encryption and Diffie-Hellman
Rather than using a single secret-key, assymetric (public key) encryption requires a *keypair*, consisting of a *public key* for encryption and a *private-key* for decryption. Data that is encrypted using a given public key can only be decrypted using the corresponding private key.
The public key is not confidential and can be shared on e.g. a website or keyserver. This allows anyone to send somebody a secure message by encrypting it with the receivers public key. The encrypted message will only be readable by the owner of the corresponding private key.
```{r}
# Create keypair
key <- keygen()
pub <- pubkey(key)
# Encrypt message for receiver using his/her public key
msg <- serialize(iris, NULL)
ciphertext <- simple_encrypt(msg, pub)
# Receiver decrypts with his/her private key
out <- simple_decrypt(ciphertext, key)
identical(msg, out)
```
How does this work? Public key encryption makes use of [Diffie-Hellman](http://mathworld.wolfram.com/Diffie-HellmanProtocol.html) (D-H): a method which allows two parties that have no prior knowledge of each other to jointly establish a shared secret key over an insecure channel. In the most simple case, both parties generate a temporary keypair and exchange their public key over the insecure channel. Then both parties use the D-H function to calculcate the (same) shared secret key by combining their own private key with the other person's public key:
```{r}
# Bob generates keypair
bob_key <- keygen()
bob_pubkey <- pubkey(bob_key)
# Alice generates keypair
alice_key <- keygen()
alice_pubkey <- pubkey(alice_key)
# After Bob and Alice exchange pubkey they can both derive the secret
alice_secret <- diffie_hellman(alice_key, bob_pubkey)
bob_secret <- diffie_hellman(bob_key, alice_pubkey)
identical(alice_secret, bob_secret)
```
Once the shared secret has been established, both parties can discard their temporary public/private key and use the shared secret to start encrypting communications with symmetric encryption as discussed earlier. Because the shared secret cannot be calculated using only the public keys, the process is safe from eavesdroppers.
The classical [Diffie-Hellman method](http://mathworld.wolfram.com/Diffie-HellmanProtocol.html) is based on the discrete logarithm problem with large prime numbers. Sodium uses [curve25519](http://cr.yp.to/ecdh/curve25519-20060209.pdf), a state-of-the-art D-H function by Daniel Bernsteinan designed for use with the elliptic curve Diffie–Hellman (ECDH) key agreement scheme.
sodium/inst/doc/crypto101.R 0000644 0001762 0000144 00000006565 13063263647 015207 0 ustar ligges users ## ---- echo = FALSE, message = FALSE--------------------------------------
knitr::opts_chunk$set(comment = "")
library(sodium)
# hack for printable bits
random <- function(n = 1){
if(n != nchar("TTIP is evil"))
return(sodium::random(n))
repeat {
x <- sodium::random(n)
y <- base::xor(charToRaw("TTIP is evil"), x)
if(all(c(x,y) != 0)) return(x)
}
}
## ------------------------------------------------------------------------
# XOR two (8bit) bytes 'x' and 'y'
x <- as.raw(0x7a)
y <- as.raw(0xe4)
z <- base::xor(x, y)
dput(z)
# Show the bits in each byte
cbind(x = rawToBits(x), y = rawToBits(y), z = rawToBits(z))
## ------------------------------------------------------------------------
# Encrypt message using random one-time-pad
msg <- charToRaw("TTIP is evil")
one_time_pad <- random(length(msg))
ciphertext <- base::xor(msg, one_time_pad)
# It's really encrypted
rawToChar(ciphertext)
# Decrypt with same pad
rawToChar(base::xor(ciphertext, one_time_pad))
## ------------------------------------------------------------------------
password <- "My secret passphrase"
key <- hash(charToRaw(password))
nonce <- random(8)
chacha20(size = 20, key, nonce)
## ------------------------------------------------------------------------
salsa20(size = 20, key, nonce)
## ------------------------------------------------------------------------
# Illustrative example.
sha256_ctr <- function(size, key, nonce){
n <- ceiling(size/32)
output <- raw()
for(i in 1:n){
counter <- packBits(intToBits(i))
block <- sha256(c(key, nonce, counter))
output <- c(output, block)
}
return(output[1:size])
}
## ------------------------------------------------------------------------
password <- "My secret passphrase"
key <- hash(charToRaw(password))
nonce <- random(8)
sha256_ctr(50, key, nonce)
## ------------------------------------------------------------------------
# Encrypt 'message' using 'password'
myfile <- file.path(R.home(), "COPYING")
message <- readBin(myfile, raw(), file.info(myfile)$size)
passwd <- charToRaw("My secret passphrase")
## ------------------------------------------------------------------------
# Basic secret key encryption
key <- hash(passwd)
nonce8 <- random(8)
stream <- chacha20(length(message), key, nonce8)
ciphertext <- base::xor(stream, message)
## ------------------------------------------------------------------------
# Decrypt with the same key
key <- hash(charToRaw("My secret passphrase"))
stream <- chacha20(length(ciphertext), key, nonce8)
out <- base::xor(ciphertext, stream)
# Print part of the message
cat(substring(rawToChar(out), 1, 120))
## ------------------------------------------------------------------------
# Create keypair
key <- keygen()
pub <- pubkey(key)
# Encrypt message for receiver using his/her public key
msg <- serialize(iris, NULL)
ciphertext <- simple_encrypt(msg, pub)
# Receiver decrypts with his/her private key
out <- simple_decrypt(ciphertext, key)
identical(msg, out)
## ------------------------------------------------------------------------
# Bob generates keypair
bob_key <- keygen()
bob_pubkey <- pubkey(bob_key)
# Alice generates keypair
alice_key <- keygen()
alice_pubkey <- pubkey(alice_key)
# After Bob and Alice exchange pubkey they can both derive the secret
alice_secret <- diffie_hellman(alice_key, bob_pubkey)
bob_secret <- diffie_hellman(bob_key, alice_pubkey)
identical(alice_secret, bob_secret)
sodium/inst/doc/intro.rmd 0000644 0001762 0000144 00000017506 13063263647 015156 0 ustar ligges users ---
title: "Sodium: A Modern and Easy-to-Use Crypto Library"
output:
html_document:
toc: false
date: "`r Sys.Date()`"
vignette: >
%\VignetteIndexEntry{Introduction to Sodium for R}
%\VignetteEngine{knitr::rmarkdown}
\usepackage[utf8]{inputenc}
---
```{r, echo = FALSE, message = FALSE}
knitr::opts_chunk$set(comment = "")
library(sodium)
```
The sodium R package provides bindings to [libsodium](https://download.libsodium.org/doc/): a modern, easy-to-use software library for encryption, decryption, signatures, password hashing and more.
The goal of Sodium is to provide the core operations needed to build higher-level cryptographic tools. It is not intended for implementing standardized protocols such as TLS, SSH or GPG. Sodium only supports a limited set of state-of-the-art elliptic curve methods, resulting in a simple but very powerful tool-kit for building secure applications.
| | Authenticated Encryption | Encryption only | Authentication only |
|-----------------------------:|:--------------------------------:|:-----------------------------------:|:--------------------------:|
| __Symmetric__ *(secret key)*: | [`data_encrypt` / `data_decrypt`](#secret-key-encryption) | | [`data_tag`](#secret-key-authentication) |
| __Asymmetric__ *(public+private key)*: | [`auth_encrypt` / `auth_decrypt`](#public-key-authenticated-encryption) | [`simple_encrypt` / `simple_decrypt`](#public-key-encryption) | [`sig_sign` / `sig_verify`](#public-key-authentication-signatures) |
| | | | |
### Using Sodium
All Sodium functions operate on binary data, called 'raw' vectors in R. Use `charToRaw` and `rawToChar` to convert between strings and raw vectors. Alternatively `hex2bin` and `bin2hex` can convert between binary data to strings in hex notation:
```{r}
test <- hash(charToRaw("test 123"))
str <- bin2hex(test)
print(str)
hex2bin(str)
```
### Random data generator
The `random()` function generates n bytes of unpredictable data, suitable for creating secret keys.
```{r}
secret <- random(8)
print(secret)
```
Implementation is platform specific, see the [docs](https://download.libsodium.org/doc/generating_random_data/index.html) for details.
### Hash functions
Sodium has several hash functions including `hash()`, `shorthash()`, `sha256()`, `sha512` and `scrypt()`. The generic `hash()` is usually recommended. It uses [blake2b](https://download.libsodium.org/doc/hashing/generic_hashing.html) with a configurable size between 16 bytes (128bit) and 64 bytes (512bit).
```{r}
# Generate keys from passphrase
passphrase <- charToRaw("This is super secret")
hash(passphrase)
hash(passphrase, size = 16)
hash(passphrase, size = 64)
```
The `shorthash()` function is a special 8 byte (64 bit) hash based on [SipHash-2-4](https://download.libsodium.org/doc/hashing/short-input_hashing.html). The output of this function is only 64 bits (8 bytes). It is useful for in e.g. Hash tables, but it should not be considered collision-resistant.
### Secret key encryption
Symmetric encryption uses the same secret key for both encryption and decryption. It is mainly useful for encrypting local data, or as a building block for more complex methods.
Most encryption methods require a `nonce`: a piece of non-secret unique data that is used to randomize the cipher. This allows for safely using the same `key` for encrypting multiple messages. The nonce should be stored or shared along with the ciphertext.
```{r}
key <- hash(charToRaw("This is a secret passphrase"))
msg <- serialize(iris, NULL)
# Encrypt with a random nonce
nonce <- random(24)
cipher <- data_encrypt(msg, key, nonce)
# Decrypt with same key and nonce
orig <- data_decrypt(cipher, key, nonce)
identical(iris, unserialize(orig))
```
Because the secret has to be known by all parties, symmetric encryption by itself is often impractical for communication with third parties. For this we need asymmetric (public key) methods.
### Secret key authentication
Secret key authentication is called tagging in Sodium. A tag is basically a hash of the data together with a secret key.
```{r}
key <- hash(charToRaw("This is a secret passphrase"))
msg <- serialize(iris, NULL)
mytag <- data_tag(msg, key)
```
To verify the integrity of the data at a later point in time, simply re-calculate the tag with the same key:
```{r}
stopifnot(identical(mytag, data_tag(msg, key)))
```
The secret key protects against forgery of the data+tag by an intermediate party, as would be possible with a regular checksum.
### Public key encryption
Where symmetric methods use the same secret key for encryption and decryption, asymmetric methods use a key-pair consisting of a public key and private key. The private key is secret and only known by its owner. The public key on the other hand can be shared with anyone. Public keys are often published on the user's website or posted in public directories or keyservers.
```{r}
key <- keygen()
pub <- pubkey(key)
```
In public key encryption, data encrypted with a public key can only be decrypted using the corresponding private key. This allows anyone to send somebody a secure message by encrypting it with the receivers public key. The encrypted message will only be readable by the owner of the corresponding private key.
```{r}
# Encrypt message with pubkey
msg <- serialize(iris, NULL)
ciphertext <- simple_encrypt(msg, pub)
# Decrypt message with private key
out <- simple_decrypt(ciphertext, key)
stopifnot(identical(out, msg))
```
### Public key authentication (signatures)
Public key authentication works the other way around. First, the owner of the private key creates a 'signature' (an authenticated checksum) for a message in a way that allows anyone who knows his/her public key to verify the integrity of the message and identity of the sender.
Currently sodium requires a different type of key-pair for signatures (ed25519) than for encryption (curve25519).
```{r}
# Generate signature keypair
key <- sig_keygen()
pubkey <- sig_pubkey(key)
# Create signature with private key
msg <- serialize(iris, NULL)
sig <- sig_sign(msg, key)
print(sig)
# Verify a signature from public key
sig_verify(msg, sig, pubkey)
```
Signatures are useful when the message itself is not confidential but integrity is important. A common use is for software repositories where to include an index file with checksums for all packages, signed by the repository maintainer. This allows client package managers to verify that the binaries were not manipulated by intermediate parties during the distribution process.
### Public key authenticated encryption
Authenticated encryption implements best practices for secure messaging. It requires that both sender and receiver have a keypair and know each other's public key. Each message gets authenticated with the key of the sender and encrypted with the key of the receiver.
```{r}
# Bob's keypair:
bob_key <- keygen()
bob_pubkey <- pubkey(bob_key)
# Alice's keypair:
alice_key <- keygen()
alice_pubkey <- pubkey(alice_key)
# Bob sends encrypted message for Alice:
msg <- charToRaw("TTIP is evil")
ciphertext <- auth_encrypt(msg, bob_key, alice_pubkey)
# Alice verifies and decrypts with her key
out <- auth_decrypt(ciphertext, alice_key, bob_pubkey)
stopifnot(identical(out, msg))
# Alice sends encrypted message for Bob
msg <- charToRaw("Let's protest")
ciphertext <- auth_encrypt(msg, alice_key, bob_pubkey)
# Bob verifies and decrypts with his key
out <- auth_decrypt(ciphertext, bob_key, alice_pubkey)
stopifnot(identical(out, msg))
```
Note that even though public keys are not confidential, you should not exchange them over the same insecure channel you are trying to protect. If the connection is being tampered with, the attacker could simply replace the key with another one to hijack the interaction.
sodium/src/ 0000755 0001762 0000144 00000000000 13067251130 012337 5 ustar ligges users sodium/src/secret.c 0000644 0001762 0000144 00000003744 13067251130 014000 0 ustar ligges users #include