# digest

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##### Create hash function digests for arbitrary R objects

The digest function applies a cryptographical hash function to arbitrary R objects. By default, the objects are internally serialized, and either one of the currently implemented MD5 and SHA-1 hash functions algorithms can be used to compute a compact digest of the serialized object.

In order to compare this implementation with others, serialization of the input argument can also be turned off in which the input argument must be a character string for which its digest is returned.

Keywords
misc
##### Usage
digest(object, algo=c("md5", "sha1", "crc32", "sha256", "sha512",
"xxhash32", "xxhash64", "murmur32"), serialize=TRUE, file=FALSE,
length=Inf, skip="auto", ascii=FALSE, raw=FALSE, seed=0,
errormode=c("stop","warn","silent"),
serializeVersion=.getSerializeVersion())
##### Arguments
object

An arbitrary R object which will then be passed to the serialize function, unless the serialize argument is set to FALSE.

algo

The algorithms to be used; currently available choices are md5, which is also the default, sha1, crc32, sha256, sha512, xxhash32, xxhash64 and murmur32.

serialize

A logical variable indicating whether the object should be serialized using serialize (in ASCII form). Setting this to FALSE allows to compare the digest output of given character strings to known control output. It also allows the use of raw vectors such as the output of non-ASCII serialization.

file

A logical variable indicating whether the object is a file name or a file name if object is not specified.

length

Number of characters to process. By default, when length is set to Inf, the whole string or file is processed.

skip

Number of input bytes to skip before calculating the digest. Negative values are invalid and currently treated as zero. Special value "auto" will cause serialization header to be skipped if serialize is set to TRUE (the serialization header contains the R version number thus skipping it allows the comparison of hashes across platforms and some R versions).

ascii

This flag is passed to the serialize function if serialize is set to TRUE, determining whether the hash is computed on the ASCII or binary representation.

raw

A logical variable with a default value of FALSE, implying digest returns digest output as ASCII hex values. Set to TRUE to return digest output in raw (binary) form. Note that this option is supported by most but not all of the implemented hashing algorithms

seed

an integer to seed the random number generator. This is only used in the xxhash32, xxhash64 and murmur32 functions and can be used to generate additional hashes for the same input if desired.

errormode

A character value denoting a choice for the behaviour in the case of error: ‘stop’ aborts (and is the default value), ‘warn’ emits a warning and returns NULL and ‘silent’ suppresses the error and returns an empty string.

serializeVersion

An integer value specifying the internal version of the serialization format, with 2 being the default; see serialize for details. The serializeVersion field of option can also be used to set a different value.

##### Details

Cryptographic hash functions are well researched and documented. The MD5 algorithm by Ron Rivest is specified in RFC 1321. The SHA-1 algorithm is specified in FIPS-180-1, SHA-2 is described in FIPS-180-2.

For md5, sha-1 and sha-256, this R implementation relies on standalone implementations in C by Christophe Devine. For crc32, code from the zlib library by Jean-loup Gailly and Mark Adler is used.

For sha-512, a standalone implementation from Aaron Gifford is used.

For xxhash32 and xxhash64, the reference implementation by Yann Collet is used.

For murmur32, the progressive implementation by Shane Day is used.

Please note that this package is not meant to be used for cryptographic purposes for which more comprehensive (and widely tested) libraries such as OpenSSL should be used. Also, it is known that crc32 is not collision-proof. For sha-1, recent results indicate certain cryptographic weaknesses as well. For more details, see for example http://www.schneier.com/blog/archives/2005/02/cryptanalysis_o.html.

##### Value

The digest function returns a character string of a fixed length containing the requested digest of the supplied R object. This string is of length 32 for MD5; of length 40 for SHA-1; of length 8 for CRC32 a string; of length 8 for for xxhash32; of length 16 for xxhash64; and of length 8 for murmur32.

##### References

SHA-1: https://en.wikipedia.org/wiki/SHA-1. SHA-256: https://csrc.nist.gov/publications/fips/fips180-2/fips180-2withchangenotice.pdf. CRC32: The original reference webpage at rocksoft.com has vanished from the web; see https://en.wikipedia.org/wiki/Cyclic_redundancy_check for general information on CRC algorithms.

http://www.aarongifford.com/computers/sha.html for the integrated C implementation of sha-512.

The page for the code underlying the C functions used here for sha-1 and md5, and further references, is no longer accessible. Please see https://en.wikipedia.org/wiki/SHA-1 and https://en.wikipedia.org/wiki/MD5.

http://zlib.net for documentation on the zlib library which supplied the code for crc32.

http://en.wikipedia.org/wiki/SHA_hash_functions for documentation on the sha functions.

https://github.com/Cyan4973/xxHash for documentation on the xxHash functions.

https://github.com/aappleby/smhasher for documentation on MurmurHash.

serialize, md5sum

• digest
##### Examples
# NOT RUN {
## Standard RFC 1321 test vectors
md5Input <-
c("",
"a",
"abc",
"message digest",
"abcdefghijklmnopqrstuvwxyz",
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789",
paste("12345678901234567890123456789012345678901234567890123456789012",
"345678901234567890", sep=""))
md5Output <-
c("d41d8cd98f00b204e9800998ecf8427e",
"0cc175b9c0f1b6a831c399e269772661",
"900150983cd24fb0d6963f7d28e17f72",
"f96b697d7cb7938d525a2f31aaf161d0",
"c3fcd3d76192e4007dfb496cca67e13b",
"d174ab98d277d9f5a5611c2c9f419d9f",
"57edf4a22be3c955ac49da2e2107b67a")

for (i in seq(along=md5Input)) {
md5 <- digest(md5Input[i], serialize=FALSE)
stopifnot(identical(md5, md5Output[i]))
}

sha1Input <-
c("abc", "abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq")
sha1Output <-
c("a9993e364706816aba3e25717850c26c9cd0d89d",
"84983e441c3bd26ebaae4aa1f95129e5e54670f1")

for (i in seq(along=sha1Input)) {
sha1 <- digest(sha1Input[i], algo="sha1", serialize=FALSE)
stopifnot(identical(sha1, sha1Output[i]))
}

crc32Input <-
c("abc",
"abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq")
crc32Output <-
c("352441c2",
"171a3f5f")

for (i in seq(along=crc32Input)) {
crc32 <- digest(crc32Input[i], algo="crc32", serialize=FALSE)
stopifnot(identical(crc32, crc32Output[i]))
}

sha256Input <-
c("abc",
"abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq")
sha256Output <-
"248d6a61d20638b8e5c026930c3e6039a33ce45964ff2167f6ecedd419db06c1")

for (i in seq(along=sha256Input)) {
sha256 <- digest(sha256Input[i], algo="sha256", serialize=FALSE)
stopifnot(identical(sha256, sha256Output[i]))
}

# SHA 512 example
sha512Input <-
c("abc",
"abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq")
sha512Output <-
c(paste("ddaf35a193617abacc417349ae20413112e6fa4e89a97ea20a9eeee64b55d39a",
"2192992a274fc1a836ba3c23a3feebbd454d4423643ce80e2a9ac94fa54ca49f",
sep=""),
paste("204a8fc6dda82f0a0ced7beb8e08a41657c16ef468b228a8279be331a703c335",
sep=""))

for (i in seq(along=sha512Input)) {
sha512 <- digest(sha512Input[i], algo="sha512", serialize=FALSE)
stopifnot(identical(sha512, sha512Output[i]))
}

## xxhash32 example
xxhash32Input <-
c("abc",
"abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq",
"")
xxhash32Output <-
c("32d153ff",
"89ea60c3",
"02cc5d05")

for (i in seq(along=xxhash32Input)) {
xxhash32 <- digest(xxhash32Input[i], algo="xxhash32", serialize=FALSE)
cat(xxhash32, "\n")
stopifnot(identical(xxhash32, xxhash32Output[i]))
}

## xxhash64 example
xxhash64Input <-
c("abc",
"abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq",
"")
xxhash64Output <-
"f06103773e8585df",
"ef46db3751d8e999")

for (i in seq(along=xxhash64Input)) {
xxhash64 <- digest(xxhash64Input[i], algo="xxhash64", serialize=FALSE)
cat(xxhash64, "\n")
stopifnot(identical(xxhash64, xxhash64Output[i]))
}

## these outputs were calculated using mmh3 python package
murmur32Input <-
c("abc",
"abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq",
"")
murmur32Output <-
c("b3dd93fa",
"ee925b90",
"00000000")

for (i in seq(along=murmur32Input)) {
murmur32 <- digest(murmur32Input[i], algo="murmur32", serialize=FALSE)
cat(murmur32, "\n")
stopifnot(identical(murmur32, murmur32Output[i]))
}

# example of a digest of a standard R list structure
digest(list(LETTERS, data.frame(a=letters[1:5], b=matrix(1:10,ncol=2))))

# test 'length' parameter and file input
fname <- file.path(R.home(),"COPYING")
for (alg in c("sha1", "md5", "crc32")) {
# partial file
h1 <- digest(x    , length=18000, algo=alg, serialize=FALSE)
h2 <- digest(fname, length=18000, algo=alg, serialize=FALSE, file=TRUE)
h3 <- digest( substr(x,1,18000) , algo=alg, serialize=FALSE)
stopifnot( identical(h1,h2), identical(h1,h3) )
# whole file
h1 <- digest(x    , algo=alg, serialize=FALSE)
h2 <- digest(fname, algo=alg, serialize=FALSE, file=TRUE)
stopifnot( identical(h1,h2) )
}

# compare md5 algorithm to other tools
library(tools)
fname <- file.path(R.home(),"COPYING")
h1 <- as.character(md5sum(fname))
h2 <- digest(fname, algo="md5", file=TRUE)
stopifnot( identical(h1,h2) )

## digest is _designed_ to return one has summary per object to for a desired
## vector of digests you need to explicitly loop, which Vectorize() can do for
## you -- see this nice SO answer: https://stackoverflow.com/a/28360092/143305
vdigest <- Vectorize(digest)
v <- vdigest(1:5)     			# digest integers 1 to 5
stopifnot(identical(v[1], digest(1L)),	# check first and third result
identical(v[3], digest(3L)))

# }

Documentation reproduced from package digest, version 0.6.15, License: GPL (>= 2)

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