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Reference: /wiki/ blind signature

Introduction: The general idea of digital signature is to generate a series of digital strings that can only be generated by the sender and cannot be forged by others. This number string is also an effective proof of the authenticity of the information sent by the sender. Different from the general digital signature, the signer of blind signature does not know the specific content of the message he signed, but only proves the authenticity of the signature as a fair person at a certain moment.

Burying nose: digital signature, blind signature

Embedded cow asked: where will blind signature be used? What's the difference between blind signature and general digital signature?

Embedded cow text: the definition of blind signature;

It is a way of digital signature, and the message content is invisible to the signer before signing. Analogical example: put a carbon paper in the envelope to sign a document. When the signer signs the envelope, his signature is signed on the document through the carbon paper.

The nature of blind signature;

In addition to the general digital signature conditions, the following two attributes must be met:

The signer is invisible to the message he signed, that is, the signer does not know the specific content of the message he signed.

(2) the signature message is untraceable, that is, when the signature message is published, the signer cannot know when he signed it.

Blind signature model;

The receiver of 1 firstly performs blind transformation on the data to be signed, and sends the transformed blind data to the signatory.

After the signer signs it, it is sent to the receiver.

3. The blind signature of the signer on the original data is obtained by the blind transformation of the signature by the receiver.

Therefore, the condition 1 is satisfied. To satisfy the condition ②, the signer must not be associated with the blind data when he sees the blind signature afterwards, which is usually realized by some protocol.

The general drawing is as follows:

The blind signature protocol includes the following steps:

1, message blind. A blinds the original message M to get M', and then sends the blinded message M' to B. There are many blind processing methods. For example, a number can be randomly selected, which is called a blind factor. After the original information is digitized, the blind information can be obtained by multiplying it by the blind factor.

2. Sign the blind letter. B will use the usual digital signature method to sign Nai and send its signature SIG(m') to A. ..

3. Restore the signature. A obtains the signature and SIG(M') of the original message m from the blind signature SIG(M') by removing the blind factor. When there is a dispute in the future, when A takes out B's blind signature, and B obviously can't deny its signature, it can prove the authenticity of the original message.

Blind signature not only retains various characteristics of digital signature, but also has the following special properties:

1, blind. The content of the message is blind to the signer, and the signer cannot see the content of the message.

2. Non-traceability. The signer only knows sig(m'), but not SIG(m). Even if the signer keeps relevant data such as sig(m'), it is still difficult to find out the internal relationship between sig(m) and sig(m'), and it is impossible to trace the owner of the message M.

Background of blind signature: electronic cash.

General signature, the signer's signature to himself, must be remembered, such as when and where it was sent to whom, and he can write it down himself. However, if the signature is regarded as electronic cash, it involves the problem of anonymity.

Do you write your name on the actual bill when you use it? Of course not. Then I don't want banks to track their signatures to get users' consumption. So we designed a blind signature.

Blind signature algorithm is a digital signature algorithm, which has the following two characteristics.

1. The signer cannot see the content of the message.

2. After the signature is made public by the receiver, the signer cannot trace the signature.