2 .\" ----------------------------------------------------------------------------
3 .\" "THE BEER-WARE LICENSE" (Revision 42):
4 .\" <phk@FreeBSD.org> wrote this file. As long as you retain this notice you
5 .\" can do whatever you want with this stuff. If we meet some day, and you think
6 .\" this stuff is worth it, you can buy me a beer in return. Poul-Henning Kamp
7 .\" ----------------------------------------------------------------------------
9 .\" From: Id: mdX.3,v 1.14 1999/02/11 20:31:49 wollman Exp
20 .Nm SHA224_FileChunk ,
27 .Nm SHA256_FileChunk ,
29 .Nd calculate the FIPS 180-2 ``SHA-256'' (or SHA-224) message digest
36 .Fn SHA224_Init "SHA224_CTX *context"
38 .Fn SHA224_Update "SHA224_CTX *context" "const unsigned char *data" "size_t len"
40 .Fn SHA224_Final "unsigned char digest[32]" "SHA224_CTX *context"
42 .Fn SHA224_End "SHA224_CTX *context" "char *buf"
44 .Fn SHA224_File "const char *filename" "char *buf"
46 .Fn SHA224_FileChunk "const char *filename" "char *buf" "off_t offset" "off_t length"
48 .Fn SHA224_Data "const unsigned char *data" "unsigned int len" "char *buf"
51 .Fn SHA256_Init "SHA256_CTX *context"
53 .Fn SHA256_Update "SHA256_CTX *context" "const unsigned char *data" "size_t len"
55 .Fn SHA256_Final "unsigned char digest[32]" "SHA256_CTX *context"
57 .Fn SHA256_End "SHA256_CTX *context" "char *buf"
59 .Fn SHA256_File "const char *filename" "char *buf"
61 .Fn SHA256_FileChunk "const char *filename" "char *buf" "off_t offset" "off_t length"
63 .Fn SHA256_Data "const unsigned char *data" "unsigned int len" "char *buf"
67 functions calculate a 256-bit cryptographic checksum (digest)
68 for any number of input bytes.
69 A cryptographic checksum is a one-way
70 hash function; that is, it is computationally impractical to find
71 the input corresponding to a particular output.
75 of the input-data, which does not disclose the actual input.
82 functions are the core functions.
87 run over the data with
89 and finally extract the result using
91 which will also erase the
97 which converts the return value to a 65-character
98 (including the terminating '\e0')
99 ASCII string which represents the 256 bits in hexadecimal.
102 calculates the digest of a file, and uses
104 to return the result.
105 If the file cannot be opened, a null pointer is returned.
109 but it only calculates the digest over a byte-range of the file specified,
117 parameter is specified as 0, or more than the length of the remaining part
120 calculates the digest from
124 calculates the digest of a chunk of data in memory, and uses
126 to return the result.
135 argument can be a null pointer, in which case the returned string
138 and subsequently must be explicitly deallocated using
143 argument is non-null it must point to at least 65 characters of buffer space.
145 SHA224 is identical SHA256, except it has slightly different initialization
146 vectors, and is truncated to a shorter digest.
150 function called with a null buf argument may fail and return NULL if:
153 Insufficient storage space is available.
160 may return NULL when underlying
175 These functions appeared in
178 The core hash routines were implemented by Colin Percival based on
179 the published FIPS 180-2 standard.
181 No method is known to exist which finds two files having the same hash value,
182 nor to find a file with a specific hash value.
183 There is on the other hand no guarantee that such a method does not exist.