AES {digest}

Create AES block cipher object

Description

This creates an object that can perform the Advanced Encryption Standard (AES) block cipher.

Usage

AES(key, mode=c("ECB", "CBC", "CFB", "CTR"), IV=NULL, padding=FALSE)

Arguments

key

The key as a 16, 24 or 32 byte raw vector for AES-128, AES-192 or AES-256 respectively.

mode

The encryption mode to use. Currently only “electronic codebook” (ECB), “cipher-block chaining” (CBC), “cipher feedback” (CFB) and “counter” (CTR) modes are supported.

IV

The initial vector for CBC and CFB mode or initial counter for CTR mode.

padding

Whether or not PKCS#7 padding is used during encryption and decryption in CBC mode.

Details

The standard NIST definition of CTR mode doesn't define how the counter is updated, it just requires that it be updated with each block and not repeat itself for a long time. This implementation treats it as a 128 bit integer and adds 1 with each successive block.

Value

An object of class "AES". This is a list containing the following component functions:

encrypt(text)

A function to encrypt a text vector. The text may be a single element character vector or a raw vector. It returns the ciphertext as a raw vector.

decrypt(ciphertext, raw = FALSE)

A function to decrypt the ciphertext. In ECB mode, the same AES object can be used for both encryption and decryption, but in CBC, CFB and CTR modes a new object needs to be created, using the same initial key and IV values. Returns a single element character vector, or a raw vector if raw = TRUE.

IV()

Report on the current state of the initialization vector. As blocks are encrypted or decrypted in CBC, CFB or CTR mode, the initialization vector is updated, so both operations can be performed sequentially on subsets of the text or ciphertext.

block_size(), key_size(), mode()

Report on these aspects of the AES object.

Author(s)

The R interface was written by Duncan Murdoch. The design is loosely based on the Python Crypto implementation. The underlying AES implementation is by Christophe Devine.

References

United States National Institute of Standards and Technology (2001). "Announcing the ADVANCED ENCRYPTION STANDARD (AES)". Federal Information Processing Standards Publication 197. https://csrc.nist.gov/publications/fips/fips197/fips-197.pdf.

Morris Dworkin (2001). "Recommendation for Block Cipher Modes of Operation". NIST Special Publication 800-38A 2001 Edition.

Examples

# First in ECB mode: the repeated block is coded the same way each time
msg <- as.raw(c(1:16, 1:16))
key <- as.raw(1:16)
aes <- AES(key, mode="ECB")
aes$encrypt(msg)
aes$decrypt(aes$encrypt(msg), raw=TRUE)

# Now in CBC mode:  each encoding is different
iv <- sample(0:255, 16, replace=TRUE)
aes <- AES(key, mode="CBC", iv)
code <- aes$encrypt(msg)
code

# Need a new object for decryption in CBC mode
aes <- AES(key, mode="CBC", iv)
aes$decrypt(code, raw=TRUE)

# In CBC mode, the input length must be a multiple of 16 bytes.
# You can use `padding = TRUE` to ensure the input length is always valid.
AES(key, mode="CBC", iv, padding = TRUE)$encrypt(as.raw(1:15))

# CFB mode: IV must be the same length as the Block's block size
# Two different instances of AES are required for encryption and decryption
iv <- sample(0:255, 16, replace=TRUE)
aes <- AES(key, mode="CFB", iv)
code <- aes$encrypt(msg)
code
#decrypt
aes <-  AES(key, mode="CFB", iv)
aes$decrypt(code)


# FIPS-197 examples

hextextToRaw <- function(text) {
  vals <- matrix(as.integer(as.hexmode(strsplit(text, "")[[1]])), ncol=2, byrow=TRUE)
  vals <- vals %*% c(16, 1)
  as.raw(vals)
}

plaintext       <- hextextToRaw("00112233445566778899aabbccddeeff")

aes128key       <- hextextToRaw("000102030405060708090a0b0c0d0e0f")
aes128output    <- hextextToRaw("69c4e0d86a7b0430d8cdb78070b4c55a")
aes <- AES(aes128key)
aes128 <- aes$encrypt(plaintext)
stopifnot(identical(aes128, aes128output))
stopifnot(identical(plaintext, aes$decrypt(aes128, raw=TRUE)))

aes192key       <- hextextToRaw("000102030405060708090a0b0c0d0e0f1011121314151617")
aes192output    <- hextextToRaw("dda97ca4864cdfe06eaf70a0ec0d7191")
aes <- AES(aes192key)
aes192 <- aes$encrypt(plaintext)
stopifnot(identical(aes192, aes192output))
stopifnot(identical(plaintext, aes$decrypt(aes192, raw=TRUE)))

aes256key       <- hextextToRaw("000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f")
aes256output     <- hextextToRaw("8ea2b7ca516745bfeafc49904b496089")
aes <- AES(aes256key)
aes256 <- aes$encrypt(plaintext)
stopifnot(identical(aes256, aes256output))
stopifnot(identical(plaintext, aes$decrypt(aes256, raw=TRUE)))

# SP800-38a examples

plaintext <- hextextToRaw(paste("6bc1bee22e409f96e93d7e117393172a",
                                "ae2d8a571e03ac9c9eb76fac45af8e51",
                                "30c81c46a35ce411e5fbc1191a0a52ef",
                                "f69f2445df4f9b17ad2b417be66c3710",sep=""))
key <- hextextToRaw("2b7e151628aed2a6abf7158809cf4f3c")

ecb128output <- hextextToRaw(paste("3ad77bb40d7a3660a89ecaf32466ef97",
                                   "f5d3d58503b9699de785895a96fdbaaf",
                                   "43b1cd7f598ece23881b00e3ed030688",
                                   "7b0c785e27e8ad3f8223207104725dd4",sep=""))
aes <- AES(key)
ecb128 <- aes$encrypt(plaintext)
stopifnot(identical(ecb128, ecb128output))
stopifnot(identical(plaintext, aes$decrypt(ecb128, raw=TRUE)))

cbc128output <- hextextToRaw(paste("7649abac8119b246cee98e9b12e9197d",
                                   "5086cb9b507219ee95db113a917678b2",
                                   "73bed6b8e3c1743b7116e69e22229516",
                                   "3ff1caa1681fac09120eca307586e1a7",sep=""))
iv <- hextextToRaw("000102030405060708090a0b0c0d0e0f")
aes <- AES(key, mode="CBC", IV=iv)
cbc128 <- aes$encrypt(plaintext)
stopifnot(identical(cbc128, cbc128output))
aes <- AES(key, mode="CBC", IV=iv)
stopifnot(identical(plaintext, aes$decrypt(cbc128, raw=TRUE)))


cfb128output <- hextextToRaw(paste("3b3fd92eb72dad20333449f8e83cfb4a",
                                   "c8a64537a0b3a93fcde3cdad9f1ce58b",
                                   "26751f67a3cbb140b1808cf187a4f4df",
                                   "c04b05357c5d1c0eeac4c66f9ff7f2e6",sep=""))
aes <- AES(key, mode="CFB", IV=iv)
cfb128 <- aes$encrypt(plaintext)
stopifnot(identical(cfb128, cfb128output))
aes <- AES(key, mode="CFB", IV=iv)
stopifnot(identical(plaintext, aes$decrypt(cfb128, raw=TRUE)))


ctr128output <- hextextToRaw(paste("874d6191b620e3261bef6864990db6ce",
                                   "9806f66b7970fdff8617187bb9fffdff",
                                   "5ae4df3edbd5d35e5b4f09020db03eab",
                                   "1e031dda2fbe03d1792170a0f3009cee",sep=""))
iv <- hextextToRaw("f0f1f2f3f4f5f6f7f8f9fafbfcfdfeff")
aes <- AES(key, mode="CTR", IV=iv)
ctr128 <- aes$encrypt(plaintext)
stopifnot(identical(ctr128, ctr128output))
aes <- AES(key, mode="CTR", IV=iv)
stopifnot(identical(plaintext, aes$decrypt(ctr128, raw=TRUE)))