We can certify whether a document was created or signed before a given time with a digital time stamp.

人们可以利用安全数字时间戳来证明在某一给定的时间之前某一数字文档是否被创建或者签名。

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To certify or attest to(the validity of a signature on a document, for example)as a notary public.

本人为此项文件签字过程之见证人，特此证明。

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To certify or attest to(the validity of a signature on a document, for example)as a notary public.

公证检验或证明（如文件签字是否有效），作为公证…

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