A new time stamping method is proposed for providing proof-of-existence of electronic digital documents. Time stamping for digital documents is useful for strict log of electronic data exchange. It is critical for a trusted time stamping authority to construct a time stamping method with no single point of compromise. Distributed digital time stamping is effective for protecting a private key to be compromised. A time stamp can be obtained without producing a single private key. A digital signature for time stamping is synthesized from collected digital signatures of distributed servers. Furthermore a time stamp for a digital document combined with other digital documents is useful for protecting a time stamp to be compromised. The combined method can be applied for constructing a time stamping authority with no single point of compromise.
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