.TH surfpcs 3
.SH NAME
surfpcs \- SURF protected counter sums
.SH SYNTAX
.B #include <surfpcs.h>

void \fBsurfpcs_init\fP(&\fIs\fR,\fIseed\fR);

void \fBsurfpcs_add\fP(&\fIs\fR,\fIbuf\fR,\fIlen\fR);

void \fBsurfpcs_out\fP(&\fIs\fR,\fIh\fR);

surfpcs \fIs\fR;
.br
uint32 \fIseed\fR[32];
.br
unsigned char *\fIbuf\fR;
.br
unsigned int \fIlen\fR;
.br
unsigned char \fIh\fR[SURFPCS_LEN];
.SH DESCRIPTION
.B surfpcs
converts a character string to a 256-bit output,
under control of a 1024-bit seed.
When the seed is secret,
.B surfpcs
appears to be indistinguishable from a completely random
variable-length-to-256-bit function.

Applying
.B surfpcs
takes three steps.
First, initialize a
.B surfpcs
variable,
.IR s ,
with
.BR surfpcs_init .
The seed will be recorded inside
.IR s .

Second, feed the input to
.BR surfpcs_add .
.I buf
is a pointer to
.I len
characters of input.
You can split the input across any number of
.B surfpcs_add
calls.

Third, call
.BR surfpcs_out .
The output will be placed into
.IR h ,
an array of
.B SURFPCS_LEN
bytes.
.B SURFPCS_LEN
is 32.

To apply
.B surfpcs
to another input you must call
.B surfpcs_init
again.
.SH "SEE ALSO"
surf(3)