November 2000 - cypherpunks-legacy

Re: Schneier: When is a Signature not a Signature? When it's a chad.
by Somebody 17 Nov '00

17 Nov '00

Bruce falls into the same error he points out: attempting to devine intent rigorously. In fact there lots of ways humans have agreed to evidence agreement, and none of them are tamper proof. Much of the corporate world runs on electronically printed signatures for checks, there is a long and illustreous history of signet rings and carved chops being used as contractual evidence... His argument is equivalent to saying that we should not accept a corporate check because the computer room could have been hacked, or that King X should not accept the seal of King Y because his nemesis might have snuck in at night and borrowed it from his finger while he slept, or that Wu-san's chop had been copied by an expert carver. (and I'm certain such events have in fact occurred.) I think his only valid point is that digital signatures are not somehow better. What they do provide are 1) an interesting possibility for _remote_ contracting, and 2) a way for computing machinery to do things analogous to humans contracting with each other. Both of these are important and will likely yield lots of exciting new applications. Bruce should keep in mind that the Digital Signature Law recently enacted basically says that no signature will be deemed invalid _purely_ because it is electronic in nature. It doesn't say that computation of m^e mod n constitutes Alice's intent to sign. It does say that if Alice and Bob agree to use such a digital mechanism to evidence intent, then they may. And just as we are learning this week that a "vote" is a more ambiguous concept than we may have intuitively thought, a "signature" has _never_ been a black-and-white expression of human intent, simply one piece of evidence in a sometimes cluttered, occasionally fraudulent, and always contestable world. "R. A. Hettinga" wrote: > At 5:58 PM -0600 on 11/15/00, Bruce Schneier wrote: > > > Why Digital Signatures Are Not Signatures > > > > > > > > When first invented in the 1970s, digital signatures made an amazing > > promise: better than a handwritten signature -- unforgeable and uncopyable > > -- on a document. Today, they are a fundamental component of business in > > cyberspace. And numerous laws, state and now federal, have codified > > digital signatures into law. > > > > These laws are a mistake. Digital signatures are not signatures, and they > > can't fulfill their promise. Understanding why requires understanding how > > they work. > > > > The math is complex, but the mechanics are simple. Alice knows a secret, > > called a private key. When she wants to "sign" a document (or a message, > > or any bucket of bits), she performs a mathematical calculation using the > > document and her private key; then she appends the results of that > > calculation -- called the "signature" -- to the document. Anyone can > > "verify" the signature by performing a different calculation with the > > message and Alice's public key, which is publicly available. If the > > verification calculation checks out then Alice must have signed the > > document, because only she knows her own private key. > > > > Mathematically, it works beautifully. Semantically, it fails > > miserably. There's nothing in the description above that constitutes > > signing. In fact, calling whatever Alice creates a "digital signature" was > > probably the most unfortunate nomenclature mistake in the history of > > cryptography. > > > > In law, a signature serves to indicate agreement to, or at least > > acknowledgment of, the document signed. When a judge sees a paper document > > signed by Alice, he knows that Alice held the document in her hands, and > > has reason to believe that Alice read and agreed to the words on the > > document. The signature provides evidence of Alice's intentions. (This is > > a simplification. With a few exceptions, you can't take a signed document > > into court and argue that Alice signed it. You have to get Alice to > > testify that she signed it, or bring handwriting experts in and then it's > > your word against hers. That's why notarized signatures are used in many > > circumstances.) > > > > When the same judge sees a digital signature, he doesn't know anything > > about Alice's intentions. He doesn't know if Alice agreed to the document, > > or even if she ever saw it. > > > > The problem is that while a digital signature authenticates the document up > > to the point of the signing computer, it doesn't authenticate the link > > between that computer and Alice. This is a subtle point. For years, I > > would explain the mathematics of digital signatures with sentences like: > > "The signer computes a digital signature of message m by computing m^e mod > > n." This is complete nonsense. I have digitally signed thousands of > > electronic documents, and I have never computed m^e mod n in my entire > > life. My computer makes that calculation. I am not signing anything; my > > computer is. > > > > PGP is a good example. This e-mail security program lets me digitally sign > > my messages. The user interface is simple: when I want to sign a message I > > select the appropriate menu item, enter my passphrase into a dialog box, > > and click "OK." The program decrypts the private key with the passphrase, > > and then calculates the digital signature and appends it to my > > e-mail. Whether I like it or not, it is a complete article of faith on my > > part that PGP calculates a valid digital signature. It is an article of > > faith that PGP signs the message I intend it to. It is an article of faith > > that PGP doesn't ship a copy of my private key to someone else, who can > > then sign whatever he wants in my name. > > > > I don't mean to malign PGP. It's a good program, and if it is working > > properly it will indeed sign what I intended to sign. But someone could > > easily write a rogue version of the program that displays one message on > > the screen and signs another. Someone could write a Back Orifice plug-in > > that captures my private key and signs documents without my consent or > > knowledge. We've already seen one computer virus that attempts to steal > > PGP private keys; nastier variants are certainly possible. > > > > The mathematics of cryptography, no matter how strong, cannot bridge the > > gap between me and my computer. Because the computer is not trusted, I > > cannot rely on it to show me what it is doing or do what I tell it > > to. Checking the calculation afterwards doesn't help; the untrusted > > computer can't be relied upon to check the calculations properly. It > > wouldn't help to verify the code, because the untrusted computer is running > > the code (and probably doing the verification). It wouldn't even help to > > store the digital signature key in a secure module: the module still has to > > rely on the untrusted computer for input and output. > > > > None of this bodes well for digital signatures. Imagine Alice in court, > > answering questions about a document she signed. "I never saw it," she > > says. "Yes, the mathematics does prove that my private key signed the > > document, but I never saw it." And then an expert witness like myself is > > called to the stand, who explains to the judge that it is possible that > > Alice never saw the document, that programs can be written to sign > > documents without Alice's knowledge, and that Alice's digital signature > > doesn't really mean anything about Alice's intentions. > > > > Solving this problem requires a trusted signing computer. If Alice had a > > small hand-held computer, with its own screen and keyboard, she could view > > documents on that screen and sign them with that keyboard. As long as the > > signing computer is trusted, her signatures are trusted. (But problems > > remain. Viewing a Microsoft Word document, for example, generally involves > > the very software most responsible for welcoming a virus into the > > computer.) In this case we're no longer relying on the mathematics for > > security, but instead the hardware and software security of that trusted > > computer. > > > > This is not to say that digital signatures are useless. There are many > > instances where the insecurities discussed here are not relevant, or where > > the dollar value of the signatures is small enough not to warrant worrying > > about them. There are also instances where authenticating to the signing > > computer is good enough, and where no further authentication is > > required. And there are instances where real-world relationships can > > obviate the legal requirements that digital signatures have been asked to > > satisfy. > > > > Digital signatures prove, mathematically, that a secret value known as the > > private key was present in a computer at the time Alice's signature was > > calculated. It is a small step from that to assume that Alice entered that > > key into the computer at the time of signing. But it is a much larger step > > to assume that Alice intended a particular document to be signed. And > > without a tamperproof computer trusted by Alice, you can expect "digital > > signature experts" to show up in court contesting a lot of digital > >signatures. > > > > Comments on the new federal digital signature law: > > <http://www4.zdnet.com:80/intweek/stories/news/0,4164,2635346,00.html> > > (multipage, don't miss the others) > > <http://www4.zdnet.com:80/intweek/stories/news/0,4164,2634368,00.html> > > <http://www.infoworld.com:80/articles/hn/xml/00/10/02/001002hnesign.xml> > > <http://www.pioneerplanet.com/tech/tcv_docs/028992.htm> > > > > A survey of laws in various states and countries: > > <http://rechten.kub.nl/simone/DS-LAWSU.HTM> > > -- > ----------------- > R. A. Hettinga <mailto: rah(a)ibuc.com> > The Internet Bearer Underwriting Corporation <http://www.ibuc.com/> > 44 Farquhar Street, Boston, MA 02131 USA > "... however it may deserve respect for its usefulness and antiquity, > [predicting the end of the world] has not been found agreeable to > experience." -- Edward Gibbon, 'Decline and Fall of the Roman Empire' --- end forwarded text -- ----------------- R. A. Hettinga <mailto: rah(a)ibuc.com> The Internet Bearer Underwriting Corporation <http://www.ibuc.com/> 44 Farquhar Street, Boston, MA 02131 USA "... however it may deserve respect for its usefulness and antiquity, [predicting the end of the world] has not been found agreeable to experience." -- Edward Gibbon, 'Decline and Fall of the Roman Empire'

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Re: Public Key Infrastructure: An Artifact...
by obfuscation＠beta.freedom.net 17 Nov '00

17 Nov '00

Bram Cohen writes: > In the vast majority of cases, preventing man in the middle attacks is a > waste of time. In the sense that, in the vast majority of communications, there is no man in the middle attack being mounted? Couldn't the same thing be said of cryptography, since in the vast majority of cases there is no eavesdropping? The point in both cases is that if you construct a protocol which has weaknesses, eventually people may begin to exploit them. Building a supposedly secure crypto protocol which is weak against a man in the middle attack is an invitation to trouble. If you had reason to use cryptography in the first place, you have reason to fear a man in the middle attack. Designing against that threat is not a waste of time, it is insurance against future troubles. Ob

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CDR: Re: Public Key Infrastructure: An Artifact...
by obfuscation＠beta.freedom.net 17 Nov '00

17 Nov '00

Bram Cohen writes: > In the vast majority of cases, preventing man in the middle attacks is a > waste of time. In the sense that, in the vast majority of communications, there is no man in the middle attack being mounted? Couldn't the same thing be said of cryptography, since in the vast majority of cases there is no eavesdropping? The point in both cases is that if you construct a protocol which has weaknesses, eventually people may begin to exploit them. Building a supposedly secure crypto protocol which is weak against a man in the middle attack is an invitation to trouble. If you had reason to use cryptography in the first place, you have reason to fear a man in the middle attack. Designing against that threat is not a waste of time, it is insurance against future troubles. Ob

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Re: Schneier: Why Digital Signatures are not Signatures (was Re: CRYPTO-GRAM, November 15, 2000)
by obfuscation＠beta.freedom.net 17 Nov '00

17 Nov '00

Keep in mind that the recent E-Sign bill is not about digital signatures. It's about electronic signatures. An electronic signature doesn't necessarily have to have anything to do with cryptography. It is simply an electronic means of registering consent. This may be as simple as a mouse click, or pressing a button on your telephone keypad to indicate consent to some charge. The insecurity of digital signatures pales when we realize how little security there is in the rest of the world. Handwritten and electronic signatures are no more secure than digital ones. As an aside, the arguments against digital signatures apply to all of cryptography, and by extension to all of computing. By these arguments, we can never trust anything our computers do. We might as well toss the whole lot into the trash bin. Ob

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Re: Public Key Infrastructure: An Artifact...
by Antonomasia 17 Nov '00

17 Nov '00

From: Bram Cohen <bram(a)gawth.com> > In the vast majority of cases, preventing man in the middle attacks is a > waste of time. Half the money I spend on advertising is wasted; the trouble is, I don't know which half." Lord Leverhulme (or John Wanamaker, or Henry Ford). -- ############################################################## # Antonomasia ant(a)notatla.demon.co.uk # # See http://www.notatla.demon.co.uk/ # ##############################################################

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CDR: Re: Aces high
by George＠Orwellian.Org 17 Nov '00

17 Nov '00

White Supremacist Tim "I'd like to see a race riot" May Moroned: # Even if meant in jest, as a comment on the situation, # it undermines the basic issue of law. Like, "Needs killing."

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CDR: Re: hey ummm...
by George＠Orwellian.Org 17 Nov '00

17 Nov '00

sunder <sunder(a)sunder.net> # JONCON88(a)aol.com wrote: # > # > how do you make a stink bomb? # # Pull your head out of your ass and smell yourself. No no no. Think about these words of wise pondering by Beavis and Butthead: "Why don't boogers smell?"

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CDR: myCyberstore.com
by bela nagy 17 Nov '00

17 Nov '00

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CDR: New Scientist article re: the Riemann hypothesis (fwd)
by Jim Choate 17 Nov '00

17 Nov '00

____________________________________________________________________ He is able who thinks he is able. Buddha The Armadillo Group ,::////;::-. James Choate Austin, Tx /:'///// ``::>/|/ ravage(a)ssz.com www.ssz.com .', |||| `/( e\ 512-451-7087 -====~~mm-'`-```-mm --'- -------------------------------------------------------------------- ---------- Forwarded message ---------- Date: Tue, 14 Nov 2000 12:57:08 -0500 (EST) From: "P.J. Ponder" <ponder(a)freenet.tlh.fl.us> To: cryptography(a)c2.net Subject: New Scientist article re: the Riemann hypothesis There is an interesting article in the New Scientist about attempts to prove the Reimann Hypothesis. Alain Connes is one of the people mentioned; he's working on a method based on quantum chaos. The article doesn't mention cryptography, oddly, among the fields that might be effected if the hypothesis is proven. http://www.newscientist.com/features/features_226444.html

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CDR: RE: Aces high
by Trei, Peter 17 Nov '00

17 Nov '00

A few years ago, the Swedish parliment was divided between two parties perfectly evenly. There were quite a number of votes where tie votes were broken by coin toss. (We have some follks over from our Stockholm office. We were surprised that they were'nt more amused by our election (many outlanders are quite snide about it), and on asking, learned the above.) Peter > ---------- > From: Tim May[SMTP:tcmay@got.net] > Reply To: Tim May > Sent: Thursday, November 16, 2000 1:39 PM > To: Multiple recipients of list > Subject: Re: Aces high > > At 12:42 PM -0500 11/16/00, David Honig wrote: > >At 04:36 AM 11/16/00 -0500, Bill Stewart wrote: > >> > >>A good tomato throwing fight _would_ be a pretty appropriate > >>way to resolve this election. You can vote early and often... > > > > > > >Its a shame duelling is passe. > > > > It's sad to see so many otherwise-careful people calling for "flips > of a coin," "hands of poker," and "duels at sunrise." > > Even if meant in jest, as a comment on the situation, it undermines > the basic issue of law. > > > --Tim May > -- > (This .sig file has not been significantly changed since 1992. As the > election debacle unfolds, it is time to prepare a new one. Stay tuned.) > >

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