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25 lines
889 B
Groff
25 lines
889 B
Groff
.TH byte_starts 3
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.SH NAME
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byte_starts \- find out if a buffer starts with a string
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.SH SYNTAX
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.B #include <libowfat/byte.h>
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int \fBbyte_starts\fP(const char *\fIbuf\fR,size_t \fIbuflen\fR,const char *\fIstr\fR);
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.SH DESCRIPTION
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\fIbyte_starts\fR returns 1 if the \fIbuflen\fR>=strlen(\fIstr\fR) and the first
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strlen(\fIstr\fR) bytes of \fIbuf\fR match the contents of \fIstr\fR, or
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0 otherwise.
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This function is meant to be used in protocol parsing and with a string
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constant for \fIstr\fR and will use gcc/clang macro trickery to reduce to a call to
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\fImemcmp\fR then.
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\fIbyte_starts\fR compares as few bytes as possible. An attacker observing
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the execution timing can thus learn where the first mismatch happened.
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Use \fIbyte_equal_notimingattack\fR to compare keys, passphrases, cookies or
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hashes instead.
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.SH "SEE ALSO"
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byte_equal(3), byte_equal_notimingattack(3), byte_start(3)
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