ripem frequently asked questions archive name ripem faq last update mar about this posting this is a listing of likely questions and information about ripem a program for public key mail encryption it this faq not ripem was written and will be maintained by marc vanheyningen mvanheyn cs indiana edu it will be posted to a variety of newsgroups on a monthly basis follow up discussion specific to ripem is redirected to the group alt security ripem what s new i am now running a world wide web archive of ripem information it does not contain much of anything that isn t available elsewhere but it has convenient pointers to the most current version of this faq and some other stuff the url is http cs indiana edu ripem dir html this month s version has a fair amount of new pointers to information on patents and stuff like that i ve also reordered a few things to have a more sensible ordering i hope i don t have to edit this again soon disclaimer nothing in this faq should be considered legal advice or anything other than one layperson s opinion if you want real legal advice talk to a real lawyer preferably one with experience in patent law export regulations or whatever area of law is in question list of questions what is ripem how can i get ripem will ripem run on my machine will ripem work with my mailer what is rsa what is des what is a fingerprint like md what is pem what s this about distributing and authenticating keys isn t it a bad idea to use patented algorithms in standards like pem what about rsadsi pkp why do all ripem public keys look very similar what is pgp what about rpem what is mime what is tis pem i have this simple way to defeat the security of ripem questions and answers what is ripem ripem is a not yet complete but useful implementation of privacy enhanced mail pem ripem allows your electronic mail to have the four security facilities provided by pem disclosure protection optional originator authenticity message integrity measures and non repudiation of origin always see what is pem ripem was written primarily by mark riordan mrr scss cl msu edu most of the code is in the public domain except for the rsa routines which are a library called rsaref licensed from rsa data security inc the current version of ripem is the current version of the macintosh port of ripem is how can i get ripem ripem uses the library of cryptographic routines rsaref which is considered munitions and thus is export restricted from distribution to persons who are not citizens or permanent residents in the u s or canada without an export license no such license has been obtained nor would one likely be granted unless the rsa key exchange were shortened to bits and the symmetric cipher changed to something weaker than des there are some suggestions that this situation may change now that clinton is in office the author requests in the readme file that this law not be violated please do not export the cryptographic code in this distribution outside of the usa or canada this is a personal request from me the author of ripem and a condition of your use of ripem note that rsaref is not in the public domain and a license for it is included with the distribution you should read it before using ripem ripem is available via anonymous ftp to citizens and permanent residents in the u s from rsa com cd to rsaref and read the readme file for info note that the non rsaref portion of ripem is not a product of rsa data security incorporated they merely are helping distribute it ripem as well as some other crypt stuff has its home site on ripem msu edu which is open to non anonymous ftp for users in the u s and canada who are citizens or permanent residents to find out how to obtain access ftp there cd to pub crypt and read the file getting access for convenience binaries for many architectures are available here in addition to the full source tree will ripem run on my machine probably it has already been ported to ms dos and most flavors of unix sunos next linux aix ultrix solaris etc ports to macintosh include a standard unix style port and a rather nice mac like port written by raymond lau author of stuffit more ports are expected and help of users is invited will ripem work with my mailer probably how easy and clean the effective interface is will depend on the sophistication and modularity of the mailer though the users guide included with the distribution discusses ways to use ripem with many popular mailers including berkeley mush elm and mh code is also included in elisp to allow easy use of ripem inside gnu emacs if you make a new interface for ripem or create an improvement on one in the distribution which you believe is convenient to use secure and may be useful to others feel free to post it to alt security ripem what is rsa rsa is a crypto system which is asymmetric or public key this means that there are two different related keys one to encrypt and one to decrypt because one cannot reasonably be derived from the other you may publish your encryption or public key widely and keep your decryption or private key to yourself anyone can use your public key to encrypt a message but only you hold the private key needed to decrypt it note that the message sent with rsa is normally just the des key to the real plaintext see what is des note that the above only provides for disclosure protection for originator authenticity message integrity and non repudiation of origin services to be implemented the fingerprint of the message see what is a fingerprint like md is encrypted with the sender s private key the recipient or a dispute resolving authority can use the sender s public key to decrypt it and confirm that the message must have come from the sender and was not altered rsa was named for the three men rivest shamir and adleman who invented it to find out lots more about rsa and modern cryptography in general ftp to rsa com and look in pub faq some information also may be in sci crypt what is des des is the data encryption standard a widely used symmetric or secret key crypto system unlike rsa des uses the same key to encrypt and decrypt messages however des is much faster than rsa ripem uses both des and rsa it generates a random key and encrypts your mail with des using that key it then encrypts that key with the recipient s public rsa key and includes the result in the letter allowing the recipient to recover the des key des is sometimes considered weak because it is somewhat old and uses a key length considered too short by modern standards however it should be reasonably safe against an opponent smaller than a large corporation or government agency it is not likely that the pem standard will incorporate support for other symmetric ciphers in the near future because there is a strong feeling that pem should be stable so it can become utilized widely without early problems with interoperability what is a fingerprint like md md is a message digest algorithm produced by rsa data security inc it provides a bit fingerprint or cryptographically secure hash of the plaintext it is cryptographically secure because it is not possible in a reasonable amount of computation to produce a different plaintext which produces the same fingerprint thus instead of signing the entire message with the sender s private key only the md of the message needs to be signed for authentication md s can also be exchanged directly for authentication for example ripem public keys include an md of the public key in the file so parties wishing to confirm their keys are authentic via a separate channel merely need exchange md s of keys and verify their accuracy md is sometimes used for other purposes for example it is often used to map an input of arbitrary length to bits of data as a passphrase interpreter or cookie generator md is described in its entirety including an implementation in c in rfc there have been some recent suggestions that md may not be as strong a hash as was originally believed presumably some other hash function will be used if this is accepted as true what is pem pem is privacy enhanced mail a standard for allowing transfer of encrypted electronic mail generated over a long period of time by a working group of experts it is described in rfcs these documents have been approved and obsolete the old rfcs ripem is not really a complete implementation of pem because pem specifies certificates for authenticating keys which ripem does not handle at this time their addition is planned what s this about distributing and authenticating keys for a remote user to be able to send secure mail to you she must know your public key for you to be able to confirm that the message received came from her you must know her public key it is important that this information be accurate if a bad guy convinces her that his key is in fact yours she will send messages which he can read ripem allows for three methods of key management a central server the distributed finger servers and a flat file all three are described in the ripem users guide which is part of the distribution none of them provide perfect security the pem standard calls for key management by certificates the addition of this feature to ripem is planned but chicken egg issues still exist isn t it a bad idea to use patented algorithms in standards like pem this issue has been considered in the standards process rfc the specification for internet standards has a discussion section on what specifications for nondiscriminatory availability must be met for a patented method to be included in a standard rfc addresses this issue with regard to the patents covering public key cryptography this does not of course mean that all questions are settled or that everyone is in agreement an interesting exchange on the use of patented algorithms in standards with regard to public key cryptography is in the league for programming freedom archive available via ftp ftp uu net doc lpf in the files bidzos letter and bidzos response amusingly the lpf files on ftp uu net are compressed with a patented algorithm what about rsadsi pkp rsa data security inc rsadsi is a california based company specializing in cryptographic technologies public key partners is a firm which holds exclusive sub licensing rights of the following u s patents and all of their corresponding foreign patents cryptographic apparatus and method diffie hellman no public key cryptographic apparatus and method hellman merkle no cryptographic communications system and method rsa no exponential cryptographic apparatus and method hellman pohlig no pkp claims these four patents cover all known methods of public key cryptography the two businesses are rather closely related for example the same person jim bidzos is president of both of them pkp has licensed this technology to a considerable number of companies ibm dec motorola at t lotus for use in their products pkp has also threatened and filed lawsuits defending their patents ripem was originally created with no connection to rsadsi other than its use of the rsaref library and for no reason other than its author s desire to see widespread use of public key cryptography however after the ball started rolling people at rsadsi got interested rsadsi decided to carry ripem on its ftp site and some people there started making their own ripem keys and contributing code ripem even won the best application built on rsaref in award why do all ripem public keys look very similar ripem public keys begin with a pkcs public key cryptography standards identifier describing various characteristics about the key so the first bunch of characters in your key may be the same as those of lots of other people s keys this does not mean your keys are similar but only that they are the same class of key were generated with the same program are of the same length etc what is pgp pgp is another cryptographic mail program called pretty good privacy pgp has been around longer than ripem and works somewhat differently pgp is not compatible with ripem in any way though pgp does also use rsa a few major differences between pgp and ripem pgp has more key management features particularly for users without a direct network connection ripem conforms to the pem rfcs and thus has a greater probability of working with other pem software pgp makes no attempt to be compatible with anything other than itself ripem uses rsaref a library of rsa routines from rsadsi which comes with a license allowing noncommercial use pgp uses its own implementation of rsa pkp claims that it is a violation of its patents to make use or sell pgp in the u s or canada without either a license or written permission see disclaimer see what about rsadsi pkp phil zimmermann the author of pgp stopped distributing it after being threatened with legal action he believed that a licensing scheme could be arranged but it hasn t happened and there seems little prospect of it happening in the future he acknowledges in the pgp user s guide in fact if you live in the usa and you are not a federal agency you shouldn t actually run pgp on your computer because public key partners wants to forbid you from running my software pgp is contraband both pgp and ripem are export restricted and cannot be sent outside the u s and canada without an export license however pgp already exists on many ftp sites in europe and other places whether you use pgp or ripem or whatever the documentation to pgp is recommended reading to anyone interested in such issues unfortunately it s not distributed separately from the program which can be difficult to find in the u s on ftp sites due to liability concerns what about rpem rpem stands for rabin privacy enhanced mail it was similar to ripem but used a public key cipher invented by rabin which is not rsa in an attempt to avoid the patents on public key systems it was written by mark riordan who later wrote ripem its distribution was halted when contrary to the beliefs of many including rabin pkp claimed that their patents were broad enough to cover the cipher employed this claim is not universally accepted but was not challenged for pragmatic reasons rpem is not really used anymore it is not compatible with ripem or pgp what is mime mime stands for multipurpose internet mail extensions and is described in rfc you can find out about it in the newsgroup comp mail mime a faq exists on it how pem should interact with mime is not yet entirely clear some people use the stopgap solution of having a mime type application x ripem in order to send ripem messages as mime ones i hope some standards will emerge draft internet documents exist on the matter what is tis pem trusted information systems is working on a version of privacy enhanced mail for general availability last i heard it was rumored to be integrated into an existing mail user agent mh rather than a stand alone system and in beta test i don t know much more than that i have this simple way to defeat the security of ripem you may wish to check the companion post ripem attacks which discusses some of the more obvious attacks on ripem s security and what procedures will minimize the risk ripem s main weak area is probably key distribution
