Financial Cryptography Update: Digitally-Signed Mail in e-Commerce - FC05
survey
March 25, 2005
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http://www.financialcryptography.com/mt/archives/000414.html
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In a paper last month at FC05, Garfinkel and friends reported on an
interesting survey conducted in two communities of merchants, one which
received signed email from a supplier, and one which did not. This was
an unusual chance to test two groups distinguished by usage of a crypto
tool.
The biggest result to my mind is that users simply didn't as a body
understand what the signed emails were all about. Even though these
merchants were dealing with valuable transactions, the group that was
receiving signed email only did a little better than the control group
in knowing it (33% as opposed to 20%). This is a confusion that I'd
expect, I recently installed a good cert into my Thunderbird and I
still cannot send out signed or encrypted email using S/MIME (I forget
why).
It's a very valuable survey, and welcome addition to the work of Ping,
Friedman, et al, and of course Simson Garfinkel's thesis. I've copied
the Conclusion below as anyone involved with email or user security
should be aware of how real systems meet real users.
But there is one area where I take exception at. Garfinkel el al
believe that commercial entities "should immediately adopt the practice
of digitally-signing their mail to customers with S/MIME signatures
using a certificate signed by a widely-published CA such as VeriSign."
Strongly Disagree! As there is nothing in the paper that indicates the
meaning of a digital signature, this is a bad recommendation. Are they
asking merchants to take on unlimited liability? Is this a simply a
protection against forged emails? Or a checksum against network
corruption? Without some thought as to what it is the merchant is
promising, I'd recommend that signing be left off.
(Encryption, on the other hand, is fine. We can never have enough
encryption. But this survey didn't cover that.)
http://fc05.ifca.ai/p15.pdf
Views, Reactions and Impact of Digitally-Signed Mail in e-Commerce.
Abstract. We surveyed 470 Amazon.com merchants regarding their
experience, knowledge and perceptions of digitally-signed email. Some
of these merchants (93) had been receiving digitally-signed VAT
invoices from Amazon for more than a year. Respondents attitudes were
measured as to the role of signed and/or sealed mail in e-commerce.
Among our findings: 25.2% of merchants thought that receipts sent by
online merchants should be digitally-signed, 13.2% thought they should
be sealed with encryption, and 33.6% thought that they should be both
signed and sealed. Statistically-significant differences between
merchants who had received the signed mail and those who had not are
noted. We conclude that Internet-based merchants should send
digitally-signed email as a best practice, even if they think that
their customers will not understand the signatures, on the grounds that
today s email systems handle such signatures automatically and the
passive exposure to signatures appears to increase acceptance and
trust.
4 Conclusions and Policy Implications
We surveyed hundreds of people actively involved in the business of
e-commerce as to their views on and experience with digitally-signed
email. Although they had not received prior notification of the fact,
some of these individuals had been receiving digitally-signed email for
more than a year. To the best of our knowledge this is the first survey
of its kind
It is widely believed that people will not use cryptographic techniques
to protect email unless it is extraordinarily easy to use. We showed
that even relatively unsophisticated computer users who do not send
digitally-signed mail nevertheless believe that it should be used to
protect the email that they themselves are sending (and to a lesser
extent, receiving as well).
We believe that digitally-signed mail could provide some measure of
defense against phishing attacks. Because attackers may try to obtain
certificates for typo or copycat names, we suggest that email clients
should indicate the difference between a certificate that had been
received many times and one that is being received for the first time
much in the way that programs implementing the popular SSH protocol
[15] alert users when a host key has changed.
We found that the majority (58.5%) of respondents did not know whether
or not the program that they used to read their mail handled
encryption, even though the vast majority (81.1%) use such mail
clients. Given this case, companies that survey their customers as to
whether or not the customers have encryption-capable mail readers are
likely to yield erroneous results.
We learned that digitally-signed mail tends to increase the recipient s
trust in the email infrastructure.We learned that despite more than a
decade of confusion over multiple standards for secure email, there are
now few if any usability barriers to receiving mail that s
digitally-signed with S/MIME signatures using established CAs.
Finally, we found that people with no obvious interest in selling or
otherwise promoting cryptographic technology believe that many email
messages sent today without protection should be either
digitally-signed, sealed with encryption, or both.
The complete survey text with simple tabulations of every question and
all respondent comments for which permission was given to quote is at
http://www. simson.net/smime-survey.html.
4.1 Recommendations
We believe that financial organizations, retailers, and other entities
doing business on the Internet should immediately adopt the practice of
digitally-signing their mail to customers with S/MIME signatures using
a certificate signed by a widely-published CA such as VeriSign.
Software for processing such messages is widely deployed. As one of our
respondents who identified himself as a very sophisticated computer
user wrote:
I use PGP, but in the several years since I have installed it I have
never used it for encrypting email, or sending signed email. I have
received and verified signed email from my ISP. I have never received
signed email from any other source (including banks, paypal, etc, which
are the organisations I would have thought would have gained most from
its use).
Given that support for S/MIME signatures is now widely deployed, we
also believe that existing mail clients and webmail systems that do not
recognize S/MIME-signed mail should be modified to do so. Our research
shows that there is significant value for users in being able to verify
signatures on signed email, even without the ability to respond to
these messages with mail that is signed or sealed.
We also believe that existing systems should be more lenient with mail
that is digitally-signed but which fails some sort of security check.
For example, Microsoft Outlook and Outlook Express give a warning if a
message is signed with a certificate that has expired, or if a
certificate is signed by a CA that is not trusted. We believe that such
warnings only confuse most users; more useful would be a warning that
indicates when there is a change in the distinguished name of a
correspondent or even when the sender s signing key changes indicating
a possible phishing attack.
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