.TH LIBHASHSUM_INIT_BLAKE256_HASHER 3 libhashsum .SH NAME libhashsum_init_blake256_hasher - initialise state for BLAKE256 hashing .SH SYNOPSIS .nf #include \fBstruct libhashsum_hasher\fP { enum libhashsum_algorithm \fIalgorithm\fP; const char *\fIalgorithm_string\fP; size_t \fIinput_block_size\fP; size_t \fIhash_size\fP; unsigned char *\fIhash_output\fP; unsigned char \fIsupports_non_whole_bytes\fP; unsigned char \fIstandard_partial_byte_input_encoding\fP; unsigned char \fIstandard_partial_byte_output_encoding\fP; size_t (*\fIprocess\fP)(struct libhashsum_hasher *\fPthis\fP, const void *\fPdata\fP, size_t \fPbytes\fP); int (*\fIfinalise_const\fP)(struct libhashsum_hasher *\fPthis\fP, const void *\fPdata\fP, size_t \fPbytes\fP, unsigned \fPextra_bits\fP); int (*\fIfinalise\fP)(struct libhashsum_hasher *\fPthis\fP, void *\fPdata\fP, size_t \fPbytes\fP, unsigned \fPextra_bits\fP, size_t \fPsize\fP); void (*\fIstretch\fP)(struct libhashsum_hasher *\fPthis\fP, int \fPskip\fP, void *\fPbuffer\fP); void (*\fIdestroy\fP)(struct libhashsum_hasher *\fPthis\fP); union libhashsum_state { /* definition omitted */ } \fIstate\fP; }; int \fBlibhashsum_init_blake256_hasher\fP(struct libhashsum_hasher *\fIhasher\fP, const void *\fIsalt\fP); .fi .PP Link with .I -lhashsum .IR "-lblake" . .SH DESCRIPTION The .B libhashsum_init_blake256_hasher function initialises .I *hasher for hashing using the cryptographic hash function BLAKE256 (a version of BLAKEs, which is a version of BLAKE), and stores hash function information and hashing functions for BLAKE256 in .IR *hasher . .PP .I salt shall be .I NULL or a buffer of 16 bytes that shall be used as a salt .RI ( NULL is equivalent to all zeroes). .PP .I hasher->algorithm will be set to .IR LIBHASHSUM_BLAKE256 . .PP .I hasher->algorithm_string will be set to .RB \(dq BLAKE256 \(dq, or (if .I salt is neither .I NULL nor all zeroes) .RB \(dq BLAKE256[salt= \fIlowercase_hexadecimal(salt)\fP ] \(dq, in which case .I hasher->algorithm_string will point to a buffer in .IR hasher->state . .PP .I hasher->input_block_size will be set to the block size BLAKE256 uses, in bytes. .PP .I hasher->hash_size will be set to the size of BLAKE256 hashes, in bytes .RI ( LIBHASHSUM_BLAKE256_HASH_SIZE ). .PP .I hasher->hash_output will be set to .IR NULL . .PP .I hasher->supports_non_whole_bytes will be set to 1 to indicate that the .I *hasher->finalise and .I *hasher->finalise_const functions support non-zero values in their .I extra_bits parameter. .PP .I hasher->process will be set to a pointer to the function to call to feed, and process, data into the hash function. Its parameter .I this shall be set to .IR hasher . Its parameter .I data parameter shall be set to the buffer of data to process, and its parameter .I bytes shall set to the number of bytes to process from .IR data . .I *hasher->process will return the number of bytes processed, which will be a multiple of .IR hasher->input_block_size no greater than .IR bytes . .PP .I hasher->finalise_const will be set to a pointer to the function to call once the entire text being hashed has been loaded, and to get the hash of the text. Its parameter .I this shall be set to .IR hasher . Its parameter .I data shall be set to the beginning of any yet unprocessed data, and its parameter .I bytes shall be set to the number of bytes to process from .IR data . Its parameter .I extra_bits shall be set to the number of bits to process from the lower bits of the incomplete byte .IR data[bytes] . The .I *hasher->finalise_const function will return 0 upon successful completion, and set .I hasher->hash_output to a pointer to a buffer in .I hasher->state containing the binary hash of the processed data. Otherwise, the function will return -1, and set .I errno to indicate the error. However, if the user has already set .I hasher->hash_output to a .RI non- NULL pointer, the function will output the binary hash to that pointer instead without redirecting .I hasher->hash_output (the application must make sure this buffer is sufficiently large). The function will failure if: .RS .TP .B EINVAL .I extra_bits is 8 or greater. .RE .PP .I hasher->finalise will be set to the pointer to a function that is an alternative to .I *hasher->finalise_const that can support zero-copy provided that the buffer input as the argument .I data is sufficiently large. The .I *hasher->finalise function may rewrite .I data and shall is does not safe to use for multiple hashers (if the same text is hashed using multiple hashers, .I *hasher->finalise_const must be used). The function's parameter .I size shall be set to the size of the buffer .IR data . .I *hasher->finalise is otherwise identical to .IR *hasher->finalise_const . .PP .I hasher->stretch will be set to .IR NULL . .PP .I hasher->destroy will be set to .IR NULL . .PP .I hasher->state will be initialised, it shall be treated as internal to the library's implementation, and may change between versions. .PP .I hasher must not be .IR NULL . .SH RETURN VALUE Upon successful completion, the .B libhashsum_init_blake256_hasher function returns 0. Otherwise, the function returns -1 and sets .I errno to indicate the error. If -1 is returned, the state of .I *hasher is undefined. .SH ERRORS The .B libhashsum_init_blake256_hasher function fails if: .TP .B ENOSYS Support was excluded at compile time. .SH EXTENDED DESCRIPTION libhashsum has normalises the all implemented hash functions to always use the least significant bits in non-whole octets, however each hash function has its unstandarded. To make it easier to create an application the use the same encoding of partial octets as other application using any particular hash function, .B struct libhashsum_hasher contains two fields: .I standard_partial_byte_input_encoding and .IR standard_partial_byte_output_encoding ; which are merely informtional. They are not set to specify how libhashsum expects and encodes non-whole octets, but rather specify how partial bytes are encoded in the reference implementation or specification of a hash function. .PP BLAKE256 always output a fixed, whole number of octets, so .I this->standard_partial_byte_output_encoding will be set to .IR LIBHASHSUM_UNSUPPORTED , however, the hash function allows non-whole octet input, and in its standard uses the most significant bits of non-whole octets, thus .I this->standard_partial_byte_input_encoding will be set to .IR LIBHASHSUM_MOST_SIGNIFICANT , which the opposite behaviour of what libhashsum implements, meaning that the last octet most be reversed when converting between the hash function's standard representation and libhashsum's representation. .SH HISTORY libhashsum 1.0. .SH SEE ALSO .BR libhashsum (7), .BR libhashsum_init_blakes_hasher (3), .BR libhashsum_init_blake_hasher (3)