SHA2(3)

SHA2(3) | Library Functions Manual | SHA2(3)

# NAME

`SHA224_Init`, `SHA224_Update`, `SHA224_Final`, `SHA224_Transform`, `SHA224_End`, `SHA224_File`, `SHA224_FileChunk`, `SHA224_Data`, `SHA256_Init`, `SHA256_Update`, `SHA256_Final`, `SHA256_Transform`, `SHA256_End`, `SHA256_File`, `SHA256_FileChunk`, `SHA256_Data`, `SHA384_Init`, `SHA384_Update`, `SHA384_Final`, `SHA384_Transform`, `SHA384_End`, `SHA384_File`, `SHA384_FileChunk`, `SHA384_Data`, `SHA512_Init`, `SHA512_Update`, `SHA512_Final`, `SHA512_Transform`, `SHA512_End`, `SHA512_File`, `SHA512_FileChunk`, `SHA512_Data` —
calculate the NIST Secure Hash Standard (version 2)

# SYNOPSIS

`#include <sys/types.h>`
`#include <sha2.h>`

void
`SHA224_Init`(SHA224_CTX *context);

void
`SHA224_Update`(SHA224_CTX *context, const uint8_t *data, size_t len);

void
`SHA224_Final`(uint8_t digest[SHA224_DIGEST_LENGTH], SHA224_CTX *context);

void
`SHA224_Transform`(uint32_t state[8], const uint8_t buffer[SHA224_BLOCK_LENGTH]);

char *
`SHA224_End`(SHA224_CTX *context, char *buf);

char *
`SHA224_File`(const char *filename, char *buf);

char *
`SHA224_FileChunk`(const char *filename, char *buf, off_t offset, off_t length);

char *
`SHA224_Data`(uint8_t *data, size_t len, char *buf);

void
`SHA256_Init`(SHA256_CTX *context);

void
`SHA256_Update`(SHA256_CTX *context, const uint8_t *data, size_t len);

void
`SHA256_Final`(uint8_t digest[SHA256_DIGEST_LENGTH], SHA256_CTX *context);

void
`SHA256_Transform`(uint32_t state[8], const uint8_t buffer[SHA256_BLOCK_LENGTH]);

char *
`SHA256_End`(SHA256_CTX *context, char *buf);

char *
`SHA256_File`(const char *filename, char *buf);

char *
`SHA256_FileChunk`(const char *filename, char *buf, off_t offset, off_t length);

char *
`SHA256_Data`(uint8_t *data, size_t len, char *buf);

void
`SHA384_Init`(SHA384_CTX *context);

void
`SHA384_Update`(SHA384_CTX *context, const uint8_t *data, size_t len);

void
`SHA384_Final`(uint8_t digest[SHA384_DIGEST_LENGTH], SHA384_CTX *context);

void
`SHA384_Transform`(uint64_t state[8], const uint8_t buffer[SHA384_BLOCK_LENGTH]);

char *
`SHA384_End`(SHA384_CTX *context, char *buf);

char *
`SHA384_File`(char *filename, char *buf);

char *
`SHA384_FileChunk`(char *filename, char *buf, off_t offset, off_t length);

char *
`SHA384_Data`(uint8_t *data, size_t len, char *buf);

void
`SHA512_Init`(SHA512_CTX *context);

void
`SHA512_Update`(SHA512_CTX *context, const uint8_t *data, size_t len);

void
`SHA512_Final`(uint8_t digest[SHA512_DIGEST_LENGTH], SHA512_CTX *context);

void
`SHA512_Transform`(uint64_t state[8], const uint8_t buffer[SHA512_BLOCK_LENGTH]);

char *
`SHA512_End`(SHA512_CTX *context, char *buf);

char *
`SHA512_File`(char *filename, char *buf);

char *
`SHA512_FileChunk`(char *filename, char *buf, off_t offset, off_t length);

char *
`SHA512_Data`(uint8_t *data, size_t len, char *buf);

# DESCRIPTION

The SHA2 functions implement the NIST Secure Hash Standard, FIPS PUB 180-2. The SHA2 functions are used to generate a condensed representation of a message called a message digest, suitable for use as a digital signature. There are four families of functions, with names corresponding to the number of bits in the resulting message digest. The SHA-224 and SHA-256 functions are limited to processing a message of less than 2^64 bits as input. The SHA-384 and SHA-512 functions can process a message of at most 2^128 - 1 bits as input.

The SHA2 functions are considered to be more secure than the sha1(3) functions with which they share a similar interface. The 224, 256, 384, and 512-bit versions of SHA2 share the same interface. For brevity, only the 256-bit variants are described below.

The `SHA256_Init`() function initializes a SHA256_CTX context for use with `SHA256_Update`(), and `SHA256_Final`(). The `SHA256_Update`() function adds data of length len to the SHA256_CTX specified by context. `SHA256_Final`() is called when all data has been added via `SHA256_Update`() and stores a message digest in the digest parameter.

The `SHA256_Transform`() function is used by `SHA256_Update`() to hash 512-bit blocks and forms the core of the algorithm. Most programs should use the interface provided by `SHA256_Init`(), `SHA256_Update`(), and `SHA256_Final`() instead of calling `SHA256_Transform`() directly.

The `SHA256_End`() function is a front end for `SHA256_Final`() which converts the digest into an ASCII representation of the digest in hexadecimal.

The `SHA256_File`() function calculates the digest for a file and returns the result via `SHA256_End`(). If `SHA256_File`() is unable to open the file, a `NULL` pointer is returned.

`SHA256_FileChunk`() behaves like `SHA256_File`() but calculates the digest only for that portion of the file starting at offset and continuing for length bytes or until end of file is reached, whichever comes first. A zero length can be specified to read until end of file. A negative length or offset will be ignored.

The `SHA256_Data`() function calculates the digest of an arbitrary string and returns the result via `SHA256_End`().

For each of the `SHA256_End`(), `SHA256_File`(), `SHA256_FileChunk`(), and `SHA256_Data`() functions the buf parameter should either be a string large enough to hold the resulting digest (e.g., `SHA224_DIGEST_STRING_LENGTH`, `SHA256_DIGEST_STRING_LENGTH`, `SHA384_DIGEST_STRING_LENGTH`, or `SHA512_DIGEST_STRING_LENGTH`, depending on the function being used) or a `NULL` pointer. In the latter case, space will be dynamically allocated via malloc(3) and should be freed using free(3) when it is no longer needed.

# EXAMPLES

The following code fragment will calculate the SHA-256 digest for the string “abc”, which is “0xba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad”.

    SHA256_CTX ctx;
    uint8_t results[SHA256_DIGEST_LENGTH];
    char *buf;
    int n;

    buf = "abc";
    n = strlen(buf);
    SHA256_Init(&ctx);
    SHA256_Update(&ctx, (uint8_t *)buf, n);
    SHA256_Final(results, &ctx);

    /* Print the digest as one long hex value */
    printf("0x");
    for (n = 0; n < SHA256_DIGEST_LENGTH; n++)
    	printf("%02x", results[n]);
    putchar('\n');

Alternately, the helper functions could be used in the following way:

    SHA256_CTX ctx;
    uint8_t output[SHA256_DIGEST_STRING_LENGTH];
    char *buf = "abc";

    printf("0x%s\n", SHA256_Data(buf, strlen(buf), output));

# SEE ALSO

cksum(1), md4(3), md5(3), rmd160(3), sha1(3)

Secure Hash Standard, FIPS PUB 180-2.

# HISTORY

The SHA2 functions appeared in OpenBSD 3.4 and NetBSD 3.0.

# AUTHORS

This implementation of the SHA functions was written by Aaron D. Gifford.

The `SHA256_End`(), `SHA256_File`(), `SHA256_FileChunk`(), and `SHA256_Data`() helper functions are derived from code written by Poul-Henning Kamp.

# CAVEATS

This implementation of the Secure Hash Standard has not been validated by NIST and as such is not in official compliance with the standard.

If a message digest is to be copied to a multi-byte type (i.e.: an array of five 32-bit integers) it will be necessary to perform byte swapping on little endian machines such as the i386, alpha, and vax.

October 9, 2018 | NetBSD 9.4