digest {digest} | R Documentation |
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.
digest(object, algo="md5", serialize=TRUE)
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 and crc32 |
serialize |
A logical variable indicating whether the object
should be serialized using serialize . Setting this to
FALSE allows to compares the digest output of given character
strings to known control output. |
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. Crc32 is described in ftp://ftp.rocksoft.com/cliens/rocksoft/papers/crc_v3.txt.
For md5 and sha-1, this R implementation relies on two standalone implementations in C by Christophe Devine. For crc32, code from the zlib library by Jean-loup Gailly and Mark Adler 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.
The digest
function returns a character string of a fixed
length containing the requested digest of the supplied R object. For
MD5, a string of length 32 is returned; for SHA-1, a string of length
40 is returned; for CRC32 a string of length 8.
NULL is returned if an bad argument for algo
had been supplied.
Dirk Eddelbuettel edd@debian.org for the R interface; Antoine Lucas for the integration of crc32; Christophe Devine for the hash function implementations for sha-1 and md5; Jean-loup Gailly and Mark Adler for crc32.
MD5: http://www.ietf.org/rfc/rfc1321.txt.
SHA-1: http://www.itl.nist.gov/fipspubs/fip180-1.htm.
CRC32: ftp://ftp.rocksoft.com/cliens/rocksoft/papers/crc_v3.txt.
http://www.cr0.net:8040/code/crypto for the underlying C functions used here for sha-1 and md5, and further references.
http://zlib.net for documentation on the zlib library which supplied the code for crc32.
## 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", NULL) sha1Output <- c("a9993e364706816aba3e25717850c26c9cd0d89d", "84983e441c3bd26ebaae4aa1f95129e5e54670f1", "34aa973cd4c4daa4f61eeb2bdbad27316534016f") for (i in seq(along=sha1Input)) { sha1 <- digest(sha1Input[i], algo="sha1", serialize=FALSE) stopifnot(identical(sha1, sha1Output[i])) } crc32Input <- c("abc", "abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq", NULL) crc32Output <- c("352441c2", "171a3f5f", "2ef80172") for (i in seq(along=crc32Input)) { crc32 <- digest(crc32Input[i], algo="crc32", serialize=FALSE) stopifnot(identical(crc32, crc32Output[i])) } # one of the FIPS- sha1 <- digest("abc", algo="sha1", serialize=FALSE) stopifnot(identical(sha1, "a9993e364706816aba3e25717850c26c9cd0d89d")) # 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))))