This document provides information for the Internet community regarding the Secure Hash Algorithm 1 (SHA-1), a hash algorithm adopted by the United States as a Federal Information Processing Standard. The document includes a detailed specification of the SHA-1 algorithm, including its implementation in C code, and discusses its security properties. The SHA-1 algorithm is designed to produce a 160-bit message digest from any length of input message, making it useful for generating digital signatures. The document also outlines two methods for computing the message digest and provides a test driver to verify the correctness of the implementation. The authors acknowledge the contributions of Tony Hansen and Garrett Wollman. The document is intended for informational purposes and does not specify any Internet standards.This document provides information for the Internet community regarding the Secure Hash Algorithm 1 (SHA-1), a hash algorithm adopted by the United States as a Federal Information Processing Standard. The document includes a detailed specification of the SHA-1 algorithm, including its implementation in C code, and discusses its security properties. The SHA-1 algorithm is designed to produce a 160-bit message digest from any length of input message, making it useful for generating digital signatures. The document also outlines two methods for computing the message digest and provides a test driver to verify the correctness of the implementation. The authors acknowledge the contributions of Tony Hansen and Garrett Wollman. The document is intended for informational purposes and does not specify any Internet standards.