---
name: "sha256"
section: "3"
platform: "macos"
package: "libmd"
version: "7"
release: "macOS 26.5"
platforms: ["freebsd", "macos"]
url: "https://new.carta.tech/sha256/3"
---

# sha256(3)

calculate the FIPS 180-2 \`\`SHA-256'' (or SHA-224) message digest

## NAME

**SHA224\_Init**, **SHA224\_Update**, **SHA224\_Final**, **SHA224\_End**, **SHA224\_File**, **SHA224\_FileChunk**, **SHA224\_Data**, **SHA256\_Init**, **SHA256\_Update**, **SHA256\_Final**, **SHA256\_End**, **SHA256\_File**, **SHA256\_FileChunk**, **SHA256\_Data** – calculate the FIPS 180-2 \`\`SHA-256'' (or SHA-224) message digest

## LIBRARY

library “libmd”

## SYNOPSIS

**#include \<sys/types.h\>**

**#include \<sha224.h\>**

*void*\

**SHA224\_Init**(*SHA224\_CTX \*context*);

*void*\

**SHA224\_Update**(*SHA224\_CTX \*context*, *const unsigned char \*data*, *size\_t len*);

*void*\

**SHA224\_Final**(*unsigned char digest\[32\]*, *SHA224\_CTX \*context*);

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

**#include \<sha256.h\>**

*void*\

**SHA256\_Init**(*SHA256\_CTX \*context*);

*void*\

**SHA256\_Update**(*SHA256\_CTX \*context*, *const unsigned char \*data*, *size\_t len*);

*void*\

**SHA256\_Final**(*unsigned char digest\[32\]*, *SHA256\_CTX \*context*);

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

## DESCRIPTION

The SHA256\_ functions calculate a 256-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. This net result is a “fingerprint” of the input-data, which does not disclose the actual input.

The **SHA256\_Init**(), **SHA256\_Update**(), and **SHA256\_Final**() functions are the core functions. Allocate an *SHA256\_CTX*, initialize it with **SHA256\_Init**(), run over the data with **SHA256\_Update**(), and finally extract the result using **SHA256\_Final**(), which will also erase the *SHA256\_CTX*.

**SHA256\_End**() is a wrapper for **SHA256\_Final**() which converts the return value to a 65-character (including the terminating '\\0') ASCII string which represents the 256 bits in hexadecimal.

**SHA256\_File**() calculates the digest of a file, and uses **SHA256\_End**() to return the result. If the file cannot be opened, a null pointer is returned. **SHA256\_FileChunk**() is similar to **SHA256\_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, **SHA256\_FileChunk**() calculates the digest from *offset* to the end of file. **SHA256\_Data**() calculates the digest of a chunk of data in memory, and uses **SHA256\_End**() to return the result.

When using **SHA256\_End**(), **SHA256\_File**(), or **SHA256\_Data**(), the *buf* argument can be a null pointer, in which case the returned string is allocated with [malloc(3)](/malloc/3.md) and subsequently must be explicitly deallocated using [free(3)](/free/3.md) after use. If the *buf* argument is non-null it must point to at least 65 characters of buffer space.

SHA224 is identical SHA256, except it has slightly different initialization vectors, and is truncated to a shorter digest.

## ERRORS

The **SHA256\_End**() function called with a null buf argument may fail and return NULL if:

- \[ENOMEM\]

  Insufficient storage space is available.

The **SHA256\_File**() and **SHA256\_FileChunk**() may return NULL when underlying [open(2)](/open/2.md), [fstat(2)](/fstat/2.md), [lseek(2)](/lseek/2.md), or SHA256\_End(2) fail.

## SEE ALSO

[md4(3)](/md4/3.md), [md5(3)](/md5/3.md), [ripemd(3)](/ripemd/3.md), [sha(3)](/sha/3.md), [sha512(3)](/sha512/3.md), [skein(3)](/skein/3.md)

## HISTORY

These functions appeared in FreeBSD 6.0.

## AUTHORS

The core hash routines were implemented by Colin Percival based on the published FIPS 180-2 standard.

## BUGS

No method is known to exist which finds two files having the same hash value, nor to find a file with a specific hash value. There is on the other hand no guarantee that such a method does not exist.