c039b52fc3
the string encoding functions touch secret key material in a bunch of places (devtls, devcap), so make sure we do not leak information by cache timing side channels, making the encoding and decoding routines constant time. we also expose the alphabets through encXchr()/decXchr() functions so caller can find the end of a encoded string before calling decode function (for libmp). the base32 encoding was broken in several ways. inputs lengths of len%5 == [2,3,4] had output truncated and it was using non-standard alphabet. documenting the alphabet change in the manpage.
70 lines
1,013 B
C
70 lines
1,013 B
C
#include <u.h>
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#include <libc.h>
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#define between(x,min,max) (((min-1-x) & (x-max-1))>>8)
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int
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enc16chr(int o)
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{
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int c;
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c = between(o, 0, 9) & ('0'+o);
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c |= between(o, 10, 15) & ('A'+(o-10));
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return c;
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}
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int
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dec16chr(int c)
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{
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int o;
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o = between(c, '0', '9') & (1+(c-'0'));
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o |= between(c, 'A', 'F') & (1+10+(c-'A'));
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o |= between(c, 'a', 'f') & (1+10+(c-'a'));
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return o-1;
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}
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int
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dec16(uchar *out, int lim, char *in, int n)
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{
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int c, w = 0, i = 0;
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uchar *start = out;
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uchar *eout = out + lim;
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while(n-- > 0){
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c = dec16chr(*in++);
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if(c < 0)
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continue;
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w = (w<<4) + c;
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i++;
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if(i == 2){
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if(out + 1 > eout)
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goto exhausted;
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*out++ = w;
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w = 0;
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i = 0;
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}
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}
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exhausted:
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return out - start;
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}
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int
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enc16(char *out, int lim, uchar *in, int n)
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{
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uint c;
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char *eout = out + lim;
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char *start = out;
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while(n-- > 0){
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c = *in++;
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if(out + 2 >= eout)
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goto exhausted;
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*out++ = enc16chr(c>>4);
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*out++ = enc16chr(c&15);
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}
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exhausted:
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*out = 0;
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return out - start;
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}
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