The MD5 Message-Digest Algorithm - rfc1321

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1、NetworkWorkingGroupR.RivestRequestforComments:1321MITLaboratoryforComputerScienceandRSADataSecurity,Inc.April1992TheMD5Message-DigestAlgorithmStatusofthisMemoThismemoprovidesinformationfortheInternetcommunity.ItdoesnotspecifyanInternetstandard.Distributionofthismemoisunlimited.Acknowlege

2、mentsWewouldliketothankDonCoppersmith,BurtKaliski,RalphMerkle,DavidChaum,andNoamNisanfornumeroushelpfulcommentsandsuggestions.TableofContents1.ExecutiveSummary12.TerminologyandNotation23.MD5AlgorithmDescription34.Summary65.DifferencesBetweenMD4andMD56References7APPENDIXA-ReferenceImpleme

3、ntation7SecurityConsiderations21Author'sAddress211.ExecutiveSummaryThisdocumentdescribestheMD5message-digestalgorithm.Thealgorithmtakesasinputamessageofarbitrarylengthandproducesasoutputa128-bit"fingerprint"or"messagedigest"oftheinput.Itisconjecturedthatitiscomputationallyinfeasibletopro

4、ducetwomessageshavingthesamemessagedigest,ortoproduceanymessagehavingagivenprespecifiedtargetmessagedigest.TheMD5algorithmisintendedfordigitalsignatureapplications,wherealargefilemustbe"compressed"inasecuremannerbeforebeingencryptedwithaprivate(secret)keyunderapublic-keycryptosystemsucha

5、sRSA.Rivest[Page1]RFC1321MD5Message-DigestAlgorithmApril1992TheMD5algorithmisdesignedtobequitefaston32-bitmachines.Inaddition,theMD5algorithmdoesnotrequireanylargesubstitutiontables;thealgorithmcanbecodedquitecompactly.TheMD5algorithmisanextensionoftheMD4message-digestalgorithm1,2].MD5is

6、slightlyslowerthanMD4,butismore"conservative"indesign.MD5wasdesignedbecauseitwasfeltthatMD4wasperhapsbeingadoptedforusemorequicklythanjustifiedbytheexistingcriticalreview;becauseMD4wasdesignedtobeexceptionallyfast,itis"attheedge"intermsofriskingsuccessfulcryptanalyticattack.MD5backsoffab

7、it,givingupalittleinspeedforamuchgreaterlikelihoodofultimatesecurity.Itincorporatessomesuggestionsmadebyvariousreviewers,andcontainsadditionaloptimizations.TheMD5algorithmisbeingplacedinthepublicdomainforreviewandpossibleadoptionasastandard.ForOSI-basedapplications,MD5'so