org.bouncycastle.pqc.crypto.falcon.FalconCodec Maven / Gradle / Ivy
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The Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for JDK 1.8 and up.
package org.bouncycastle.pqc.crypto.falcon;
class FalconCodec
{
FalconCodec()
{
}
/* see inner.h */
int modq_encode(
byte[] srcout, int out, int max_out_len,
short[] srcx, int x, int logn)
{
int n, out_len, u;
int buf;
int acc;
int acc_len;
n = 1 << logn;
for (u = 0; u < n; u++)
{
if ((srcx[x + u] & 0x0000ffff) >= 12289)
{
return 0;
}
}
out_len = ((n * 14) + 7) >> 3;
if (srcout == null)
{
return out_len;
}
if (out_len > max_out_len)
{
return 0;
}
buf = out;
acc = 0;
acc_len = 0;
for (u = 0; u < n; u++)
{
acc = (acc << 14) | (srcx[x + u] & 0xffff);
acc_len += 14;
while (acc_len >= 8)
{
acc_len -= 8;
srcout[buf++] = (byte)(acc >> acc_len);
}
}
if (acc_len > 0)
{
srcout[buf] = (byte)(acc << (8 - acc_len));
}
return out_len;
}
/* see inner.h */
int modq_decode(
short[] srcx, int x, int logn,
byte[] srcin, int in, int max_in_len)
{
int n, in_len, u;
int buf;
int acc;
int acc_len;
n = 1 << logn;
in_len = ((n * 14) + 7) >> 3;
if (in_len > max_in_len)
{
return 0;
}
buf = in;
acc = 0;
acc_len = 0;
u = 0;
while (u < n)
{
acc = (acc << 8) | (srcin[buf++] & 0xff);
acc_len += 8;
if (acc_len >= 14)
{
int w;
acc_len -= 14;
w = (acc >>> acc_len) & 0x3FFF;
if (w >= 12289)
{
return 0;
}
srcx[x + u] = (short)w;
u++;
}
}
if ((acc & ((1 << acc_len) - 1)) != 0)
{
return 0;
}
return in_len;
}
/* see inner.h */
int trim_i16_encode(
byte[] srcout, int out, int max_out_len,
short[] srcx, int x, int logn, int bits)
{
int n, u, out_len;
int minv, maxv;
int buf;
int acc, mask;
int acc_len;
n = 1 << logn;
maxv = (1 << (bits - 1)) - 1;
minv = -maxv;
for (u = 0; u < n; u++)
{
if (srcx[x + u] < minv || srcx[x + u] > maxv)
{
return 0;
}
}
out_len = ((n * bits) + 7) >> 3;
if (srcout == null)
{
return out_len;
}
if (out_len > max_out_len)
{
return 0;
}
buf = out;
acc = 0;
acc_len = 0;
mask = (1 << bits) - 1;
for (u = 0; u < n; u++)
{
acc = (acc << bits) | ((srcx[x + u] & 0xfff) & mask);
acc_len += bits;
while (acc_len >= 8)
{
acc_len -= 8;
srcout[buf++] = (byte)(acc >> acc_len);
}
}
if (acc_len > 0)
{
srcout[buf++] = (byte)(acc << (8 - acc_len));
}
return out_len;
}
/* see inner.h */
int trim_i16_decode(
short[] srcx, int x, int logn, int bits,
byte[] srcin, int in, int max_in_len)
{
int n, in_len;
int buf;
int u;
int acc, mask1, mask2;
int acc_len;
n = 1 << logn;
in_len = ((n * bits) + 7) >> 3;
if (in_len > max_in_len)
{
return 0;
}
buf = in;
u = 0;
acc = 0;
acc_len = 0;
mask1 = (1 << bits) - 1;
mask2 = 1 << (bits - 1);
while (u < n)
{
acc = (acc << 8) | (srcin[buf++] & 0xff);
acc_len += 8;
while (acc_len >= bits && u < n)
{
int w;
acc_len -= bits;
w = (acc >>> acc_len) & mask1;
w |= -(w & mask2);
if (w == -mask2)
{
/*
* The -2^(bits-1) value is forbidden.
*/
return 0;
}
w |= -(w & mask2);
srcx[x + u] = (short)w;
u++;
}
}
if ((acc & ((1 << acc_len) - 1)) != 0)
{
/*
* Extra bits in the last byte must be zero.
*/
return 0;
}
return in_len;
}
/* see inner.h */
int trim_i8_encode(
byte[] srcout, int out, int max_out_len,
byte[] srcx, int x, int logn, int bits)
{
int n, u, out_len;
int minv, maxv;
int buf;
int acc, mask;
int acc_len;
n = 1 << logn;
maxv = (1 << (bits - 1)) - 1;
minv = -maxv;
for (u = 0; u < n; u++)
{
if (srcx[x + u] < minv || srcx[x + u] > maxv)
{
return 0;
}
}
out_len = ((n * bits) + 7) >> 3;
if (srcout == null)
{
return out_len;
}
if (out_len > max_out_len)
{
return 0;
}
buf = out;
acc = 0;
acc_len = 0;
mask = (1 << bits) - 1;
for (u = 0; u < n; u++)
{
acc = (acc << bits) | ((srcx[x + u] & 0xffff) & mask);
acc_len += bits;
while (acc_len >= 8)
{
acc_len -= 8;
srcout[buf++] = (byte)(acc >>> acc_len);
}
}
if (acc_len > 0)
{
srcout[buf++] = (byte)(acc << (8 - acc_len));
}
return out_len;
}
/* see inner.h */
int trim_i8_decode(
byte[] srcx, int x, int logn, int bits,
byte[] srcin, int in, int max_in_len)
{
int n, in_len;
int buf;
int u;
int acc, mask1, mask2;
int acc_len;
n = 1 << logn;
in_len = ((n * bits) + 7) >> 3;
if (in_len > max_in_len)
{
return 0;
}
buf = in;
u = 0;
acc = 0;
acc_len = 0;
mask1 = (1 << bits) - 1;
mask2 = 1 << (bits - 1);
while (u < n)
{
acc = (acc << 8) | (srcin[buf++] & 0xff);
acc_len += 8;
while (acc_len >= bits && u < n)
{
int w;
acc_len -= bits;
w = (acc >>> acc_len) & mask1;
w |= -(w & mask2);
if (w == -mask2)
{
/*
* The -2^(bits-1) value is forbidden.
*/
return 0;
}
srcx[x + u] = (byte)w;
u++;
}
}
if ((acc & ((1 << acc_len) - 1)) != 0)
{
/*
* Extra bits in the last byte must be zero.
*/
return 0;
}
return in_len;
}
/* see inner.h */
int comp_encode(
byte[] srcout, int out, int max_out_len,
short[] srcx, int x, int logn)
{
int buf;
int n, u, v;
int acc;
int acc_len;
n = 1 << logn;
buf = out;
/*
* Make sure that all values are within the -2047..+2047 range.
*/
for (u = 0; u < n; u++)
{
if (srcx[x + u] < -2047 || srcx[x + u] > +2047)
{
return 0;
}
}
acc = 0;
acc_len = 0;
v = 0;
for (u = 0; u < n; u++)
{
int t;
int w;
/*
* Get sign and absolute value of next integer; push the
* sign bit.
*/
acc <<= 1;
t = srcx[x + u];
if (t < 0)
{
t = -t;
acc |= 1;
}
w = t;
/*
* Push the low 7 bits of the absolute value.
*/
acc <<= 7;
acc |= w & 127;
w >>>= 7;
/*
* We pushed exactly 8 bits.
*/
acc_len += 8;
/*
* Push as many zeros as necessary, then a one. Since the
* absolute value is at most 2047, w can only range up to
* 15 at this point, thus we will add at most 16 bits
* here. With the 8 bits above and possibly up to 7 bits
* from previous iterations, we may go up to 31 bits, which
* will fit in the accumulator, which is an uint32_t.
*/
acc <<= (w + 1);
acc |= 1;
acc_len += w + 1;
/*
* Produce all full bytes.
*/
while (acc_len >= 8)
{
acc_len -= 8;
if (srcout != null)
{
if (v >= max_out_len)
{
return 0;
}
srcout[buf + v] = (byte)(acc >>> acc_len);
}
v++;
}
}
/*
* Flush remaining bits (if any).
*/
if (acc_len > 0)
{
if (srcout != null)
{
if (v >= max_out_len)
{
return 0;
}
srcout[buf + v] = (byte)(acc << (8 - acc_len));
}
v++;
}
return v;
}
/* see inner.h */
int comp_decode(
short[] srcx, int x, int logn,
byte[] srcin, int in, int max_in_len)
{
int buf;
int n, u, v;
int acc;
int acc_len;
n = 1 << logn;
buf = in;
acc = 0;
acc_len = 0;
v = 0;
for (u = 0; u < n; u++)
{
int b, s, m;
/*
* Get next eight bits: sign and low seven bits of the
* absolute value.
*/
if (v >= max_in_len)
{
return 0;
}
acc = (acc << 8) | (srcin[buf + v] & 0xff);
v++;
b = acc >>> acc_len;
s = b & 128;
m = b & 127;
/*
* Get next bits until a 1 is reached.
*/
for (; ; )
{
if (acc_len == 0)
{
if (v >= max_in_len)
{
return 0;
}
acc = (acc << 8) | (srcin[buf + v] & 0xff);
v++;
acc_len = 8;
}
acc_len--;
if (((acc >>> acc_len) & 1) != 0)
{
break;
}
m += 128;
if (m > 2047)
{
return 0;
}
}
/*
* "-0" is forbidden.
*/
if (s != 0 && m == 0)
{
return 0;
}
srcx[x + u] = (short)(s != 0 ? -m : m);
}
/*
* Unused bits in the last byte must be zero.
*/
if ((acc & ((1 << acc_len) - 1)) != 0)
{
return 0;
}
return v;
}
/*
* Key elements and signatures are polynomials with small integer
* coefficients. Here are some statistics gathered over many
* generated key pairs (10000 or more for each degree):
*
* log(n) n max(f,g) std(f,g) max(F,G) std(F,G)
* 1 2 129 56.31 143 60.02
* 2 4 123 40.93 160 46.52
* 3 8 97 28.97 159 38.01
* 4 16 100 21.48 154 32.50
* 5 32 71 15.41 151 29.36
* 6 64 59 11.07 138 27.77
* 7 128 39 7.91 144 27.00
* 8 256 32 5.63 148 26.61
* 9 512 22 4.00 137 26.46
* 10 1024 15 2.84 146 26.41
*
* We want a compact storage format for private key, and, as part of
* key generation, we are allowed to reject some keys which would
* otherwise be fine (this does not induce any noticeable vulnerability
* as long as we reject only a small proportion of possible keys).
* Hence, we enforce at key generation time maximum values for the
* elements of f, g, F and G, so that their encoding can be expressed
* in fixed-width values. Limits have been chosen so that generated
* keys are almost always within bounds, thus not impacting neither
* security or performance.
*
* IMPORTANT: the code assumes that all coefficients of f, g, F and G
* ultimately fit in the -127..+127 range. Thus, none of the elements
* of max_fg_bits[] and max_FG_bits[] shall be greater than 8.
*/
final byte[] max_fg_bits = {
0, /* unused */
8,
8,
8,
8,
8,
7,
7,
6,
6,
5
};
final byte[] max_FG_bits = {
0, /* unused */
8,
8,
8,
8,
8,
8,
8,
8,
8,
8
};
/*
* When generating a new key pair, we can always reject keys which
* feature an abnormally large coefficient. This can also be done for
* signatures, albeit with some care: in case the signature process is
* used in a derandomized setup (explicitly seeded with the message and
* private key), we have to follow the specification faithfully, and the
* specification only enforces a limit on the L2 norm of the signature
* vector. The limit on the L2 norm implies that the absolute value of
* a coefficient of the signature cannot be more than the following:
*
* log(n) n max sig coeff (theoretical)
* 1 2 412
* 2 4 583
* 3 8 824
* 4 16 1166
* 5 32 1649
* 6 64 2332
* 7 128 3299
* 8 256 4665
* 9 512 6598
* 10 1024 9331
*
* However, the largest observed signature coefficients during our
* experiments was 1077 (in absolute value), hence we can assume that,
* with overwhelming probability, signature coefficients will fit
* in -2047..2047, i.e. 12 bits.
*/
final byte[] max_sig_bits = {
0, /* unused */
10,
11,
11,
12,
12,
12,
12,
12,
12,
12
};
}
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