Stuart Haber and Scott Stonnetta, cryptographers from Bell Communications Research, Inc. Bellcore in the United States, wrote in September 1991 in the Journal of Cryptology, "How to Print a Digital Document." In their paper, they first described the concept of 'timestamp' that proves reliability by timestamping digital documents. They introduced a timestamp service called "Surety" that uses a cryptographic hashing algorithm to generate unique IDs for each document, which also changes the ID each time the document changes. In addition, the ‘Surety’ invented an "unforgery" seal for all customers by invoking a "universal registry database" consisting of pooled customer seal. They also completed the first case of blockchain technology by publishing weekly newly classified hash values in a small section of the New York Times.