/[gzz]/manuscripts/bookburnings/techreport.rst
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revision 1.3 by benja, Wed Jul 16 19:06:42 2003 UTC revision 1.4 by benja, Wed Jul 16 19:45:12 2003 UTC
# Line 114  patented timestamping technology. Line 114  patented timestamping technology.
114  An "A said that B said that C said..." approach  An "A said that B said that C said..." approach
115  ===============================================  ===============================================
116    
117    We start the exposition of our system with a simplistic
118    approach based on a Trusted Third Party (TTP), an
119    actor trusted by all participants in the system.
120    
121    To sign a message, the signer contacts the TTP,
122    authenticates themselves, and submits the message
123    to be signed.
124    
125    To verify a message, the verifier contacts the TTP,
126    submitting the message and alleged signer; the TTP
127    tells the verifier whether the signer has submitted
128    this message or not.
129    
130    Clearly, this system isn't very attractive in
131    practice; not only can the TTP declare arbitrary
132    messages signed by arbitrary signers, it can also
133    "change its mind" and claim a message not signed
134    that it claimed to be signed at an earlier time.
135    
136    To make it harder for the TTP to "change its mind,"
137    we improve the above system as follows:
138    
139    - The TTP issues certificates on (signer,message)
140      pairs, stating that a given signer submitted
141      a given message. (Normally, a hash of the message
142      is included in the certificate instead of
143      the actual message itself.)
144    - Each certificate includes a cryptographic hash
145      of the previous issued certificate.
146    - At any time, the TTP publishes the hash of the
147      most recently issued certificate.
148    
149    A certificate is valid if it is connected
150    to the most recent certificate through an unbroken
151    chain of hash links.
152    
153    
154    
155    
156    
157  - Key intuition: each signer picks an *envoy*,  - Key intuition: each signer picks an *envoy*,
158    a service provider. The signer has signed something    a service provider. The signer has signed something
159    if their envoy says they have signed it.    if their envoy says they have signed it.

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