Update of "Experiment: Chainsignature"
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Artifact ID: e30dea3fc4bc90eaf6230c8dfc17fa6e210038c0
Page Name:Experiment: Chainsignature
Date: 2017-05-26 18:06:58
Original User: martin_vahi
Parent: 14ff92efb518a00258bf09a491ecc10f51778ef6 (diff)
Next 42f7cec0fc59706853caf071190d1fb3562e89e5

The purpose of a signature is to authenticate the creator of the signed object. 

In the case of blind dates, internet shopping there is nothing to authenticate at the first exchange of information, because all merchants and blind date partners are total strangers anyway. What matters is that the correspondence that follows the first exchange of information is with the same stranger, not with some other stranger. 

The Scheme

The scheme is that message M_n signature is a secure hash of a concatenation of all messages since the first message, message M_n included. If M_1 is a file with the very first message that the signer sent and M_2 is the 2. message that the signer sent, then a way to calculate the signature is:

    cat ./M_1.blob  > ./x.blob   # The ">" is required for overwriting the old x.blob .
    cat ./M_2.blob >> ./x.blob   # The ">>" in stead of the ">" is 
                                 # required to add in stead of overwriting.
    cat ./M_3.blob >> ./x.blob
    cat ./M_n.blob >> ./x.blob
    sha256sum ./x.blob > ./the_signature.txt

The M_n must be included to the signature calculation x.blob to make sure that an eavesdropper can not reuse the signature for signing its own message. To make eavesdropping more difficult, different messages might be sent through different channels. 

Optional Bootstrapping

The message M_1 might be accompanied by M_0, which might be some bitstream that is distributed as a small piece of paper with a QR-code. Given that NSA and alike do not intercept paper-mail/snail-mail without specifically targeting someone, because the cost of doing physical processing of physical letters is too high, some initial symmetric cryptography keys and the M_0 might be sent by using snail-mail.