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	libzahl.7 - libzahl - big integer library
	git clone git://git.suckless.org/libzahl
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	libzahl.7 (2304B)
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	1 .TH LIBZAHL 7 libzahl
	2 .SH NAME
	3 libzahl - Big integer library
	4 .SH ETYMOLOGY
	5 The bold uppercase \(aqZ\(aq which represents the
	6 set of all integers is derived from the german word
	7 \(aqZahlen\(aq, whose singular is \(aqZahl\(aq.
	8 .SH DESCRIPTION
	9 .B libzahl
	10 is a C library for arbitrary size integers, that
	11 aims to be usable for robust programs, and be
	12 fast.
	13 .P
	14 .B libzahl
	15 will accomplish this by using long jumps when an
	16 error is detected, rather than letting the caller
	17 also perform a check. This shall make the code in
	18 the user program cleaner too.
	19 .B libzahl
	20 will use dedicated temporary bignum integers whether
	21 possible, and necessary, for its internal calculations.
	22 .B libzahl
	23 will not deallocate allocations, but rather cache
	24 them for reuse.
	25 .P
	26 With the exception of functions working with strings,
	27 all output parameters are before the input parameters.
	28 .P
	29 Like any self-respecting big number library, libzahl
	30 supports assign values to variables that are also
	31 input variables. However, keep in mind that commutative
	32 functions are optimised for the first operand to also
	33 be the output over the second operand to also be the
	34 input. For example, \fIzadd(a,a,b)\fP should be faster
	35 than \fIzadd(a,b,a)\fP, although both are supported.
	36 Whether or not the function believe that it is more
	37 likely to occur that the input variables are different
	38 that the output variable than the output variable
	39 being the first input variable depends on the function.
	40 Some functions are implemented to believe that the
	41 first is more likely, other fucntions are implemented
	42 to believe that the latter is more likely.
	43 .SH RATIONALE
	44 GMP MP cannot be used for robust programs. LibTomMath
	45 is too slow, probably because of all memory allocations,
	46 and has an nonintuitive API. Hebimath is promising, but
	47 I think it can be done better.
	48 .SH NOTES
	49 .B libzahl
	50 is currently not thread-safe.
	51 .P
	52 You are strongly discouraged from using
	53 .B libzahl
	54 for cryptographic applications. Instead, use a library
	55 specifically targeting cryptography, otherwise, your
	56 program may be subject to side-channel attacks such as
	57 timing attacks, power-monitoring attacks, electromagnetic
	58 attacks, acoustic cryptanalysis, and data remanence
	59 attacks.
	60 .B libzahl
	61 is known to be susceptible to timing attacks and data
	62 remanence attacks.
	63 .SH SEE ALSO
	64 .BR zsetup (3)