SHA(3)

💖 SHA(3) — secure hash algorithms, but make it make sense ✨

okay so welcome to the SHA(3) page from the Library Functions Manual, bestie. This is basically the group chat for the SHA_ and SHA1_ function family. 🫶

🌸 NAME 🌸

Meet the whole squad: SHA_Init, SHA_Update, SHA_Final, SHA_End, SHA_Fd, SHA_FdChunk, SHA_File, SHA_FileChunk, SHA_Data, SHA1_Init, SHA1_Update, SHA1_Final, SHA1_End, SHA1_Fd, SHA1_FdChunk, SHA1_File, SHA1_FileChunk, and SHA1_Data — all here to calculate the FIPS 160 and 160-1 “SHA” message digests.

🫶 LIBRARY 🫶

This is the Message Digest (MD4, MD5, etc.) Support Library — aka libmd — and you link it with -lmd. iykyk.

📜 SYNOPSIS 📜

Here's the exact spellbook, no cap:

#include <sys/types.h>
#include <sha.h>

void
SHA_Init(SHA_CTX *context);

void
SHA_Update(SHA_CTX *context, const unsigned char *data, size_t len);

void
SHA_Final(unsigned char digest[20], SHA_CTX *context);

char *
SHA_End(SHA_CTX *context, char *buf);

char *
SHA_Fd(int fd, char *buf);

char *
SHA_FdChunk(int fd, char *buf, off_t offset, off_t length);

char *
SHA_File(const char *filename, char *buf);

char *
SHA_FileChunk(const char *filename, char *buf, off_t offset,
    off_t length);

char *
SHA_Data(const unsigned char *data, unsigned int len, char *buf);

void
SHA1_Init(SHA_CTX *context);

void
SHA1_Update(SHA_CTX *context, const unsigned char *data, size_t len);

void
SHA1_Final(unsigned char digest[20], SHA_CTX *context);

char *
SHA1_End(SHA_CTX *context, char *buf);

char *
SHA1_Fd(int fd, char *buf);

char *
SHA1_FdChunk(int fd, char *buf, off_t offset, off_t length);

char *
SHA1_File(const char *filename, char *buf);

char *
SHA1_FileChunk(const char *filename, char *buf, off_t offset,
    off_t length);

char *
SHA1_Data(const unsigned char *data, unsigned int len, char *buf);

💅 DESCRIPTION 💅

The SHA_ and SHA1_ functions calculate a 160-bit cryptographic checksum (digest) for any number of input bytes. A cryptographic checksum is a one-way hash function; that is, it is computationally impractical to find the input corresponding to a particular output. The net result is a “fingerprint” of the input-data, which does not disclose the actual input. 🦋

SHA (or SHA-0) is the original Secure Hash Algorithm specified in FIPS 160. It was quickly proven insecure and has been superseded by SHA-1. SHA-0 is included for compatibility purposes only. 💀

SHA1_Init(), SHA1_Update(), and SHA1_Final() are the core functions. Allocate an SHA_CTX, initialize it with SHA1_Init(), run over the data with SHA1_Update(), and finally extract the result using SHA1_Final() — which will also erase the SHA_CTX. 🧚

SHA1_End() is a wrapper for SHA1_Final() which converts the return value to a 41-character (including the terminating '\0') ASCII string which represents the 160 bits in hexadecimal. ✨

SHA1_File() calculates the digest of a file and uses SHA1_End() to return the result. If the file cannot be opened, a null pointer is returned. SHA1_FileChunk() is similar to SHA1_File(), but it only calculates the digest over a byte-range of the file specified, starting at offset and spanning length bytes. If the length parameter is specified as 0, or more than the length of the remaining part of the file, SHA1_FileChunk() calculates the digest from offset to the end of file. SHA1_Data() calculates the digest of a chunk of data in memory and uses SHA1_End() to return the result. 🍓

SHA1_Fd() and SHA1_FdChunk() are identical to their SHA1_File() and SHA1_FileChunk() counterparts, with the exception that the first argument is an fd instead of a filename. 🐚

buf tea time: when using SHA1_End(), SHA1_File(), or SHA1_Data(), the buf argument can be a null pointer. In that case the returned string is allocated with malloc(3) and subsequently must be explicitly deallocated using free(3) after use. If the buf argument is non-null it must point to at least 41 characters of buffer space. 🎀

😭 ERRORS 😭

The SHA1_End() function, when called with a null buf argument, may fail and return NULL if:

• [ENOMEM] — Insufficient storage space is available.

SHA1_File() and SHA1_FileChunk() may return NULL when underlying open(2), fstat(2), lseek(2), or SHA1_End(3) fail.

👀 SEE ALSO 👀

Go peek at these icons: md4(3), md5(3), ripemd(3), sha256(3), sha512(3), skein(3).

🕰️ HISTORY 🕰️

These functions appeared in FreeBSD 4.0. vintage but still in the chat. 🎀

👑 AUTHORS 👑

The core hash routines were implemented by Eric Young based on the published FIPS standards. king behavior. 👑

💀 BUGS 💀

🚨 Warning: the SHA1 algorithm has been proven to be vulnerable to practical collision attacks and should not be relied upon to produce unique outputs, nor should it be used as part of a new cryptographic signature scheme. periodt. 💅

xoxo, your Debian bestie 💅 — this SHA(3) page is dated February 12, 2023.