diff options
Diffstat (limited to 'crypto')
| -rw-r--r-- | crypto/gf128mul.c | 49 |
1 files changed, 32 insertions, 17 deletions
diff --git a/crypto/gf128mul.c b/crypto/gf128mul.c index c050cf6..1fde1c7 100644 --- a/crypto/gf128mul.c +++ b/crypto/gf128mul.c @@ -88,31 +88,46 @@ q(0xf8), q(0xf9), q(0xfa), q(0xfb), q(0xfc), q(0xfd), q(0xfe), q(0xff) \ } -/* Given the value i in 0..255 as the byte overflow when a field element - in GHASH is multiplied by x^8, this function will return the values that - are generated in the lo 16-bit word of the field value by applying the - modular polynomial. The values lo_byte and hi_byte are returned via the - macro xp_fun(lo_byte, hi_byte) so that the values can be assembled into - memory as required by a suitable definition of this macro operating on - the table above -*/ +/* + * Given a value i in 0..255 as the byte overflow when a field element + * in GF(2^128) is multiplied by x^8, the following macro returns the + * 16-bit value that must be XOR-ed into the low-degree end of the + * product to reduce it modulo the polynomial x^128 + x^7 + x^2 + x + 1. + * + * There are two versions of the macro, and hence two tables: one for + * the "be" convention where the highest-order bit is the coefficient of + * the highest-degree polynomial term, and one for the "le" convention + * where the highest-order bit is the coefficient of the lowest-degree + * polynomial term. In both cases the values are stored in CPU byte + * endianness such that the coefficients are ordered consistently across + * bytes, i.e. in the "be" table bits 15..0 of the stored value + * correspond to the coefficients of x^15..x^0, and in the "le" table + * bits 15..0 correspond to the coefficients of x^0..x^15. + * + * Therefore, provided that the appropriate byte endianness conversions + * are done by the multiplication functions (and these must be in place + * anyway to support both little endian and big endian CPUs), the "be" + * table can be used for multiplications of both "bbe" and "ble" + * elements, and the "le" table can be used for multiplications of both + * "lle" and "lbe" elements. + */ -#define xda_bbe(i) ( \ +#define xda_be(i) ( \ (i & 0x80 ? 0x4380 : 0) ^ (i & 0x40 ? 0x21c0 : 0) ^ \ (i & 0x20 ? 0x10e0 : 0) ^ (i & 0x10 ? 0x0870 : 0) ^ \ (i & 0x08 ? 0x0438 : 0) ^ (i & 0x04 ? 0x021c : 0) ^ \ (i & 0x02 ? 0x010e : 0) ^ (i & 0x01 ? 0x0087 : 0) \ ) -#define xda_lle(i) ( \ +#define xda_le(i) ( \ (i & 0x80 ? 0xe100 : 0) ^ (i & 0x40 ? 0x7080 : 0) ^ \ (i & 0x20 ? 0x3840 : 0) ^ (i & 0x10 ? 0x1c20 : 0) ^ \ (i & 0x08 ? 0x0e10 : 0) ^ (i & 0x04 ? 0x0708 : 0) ^ \ (i & 0x02 ? 0x0384 : 0) ^ (i & 0x01 ? 0x01c2 : 0) \ ) -static const u16 gf128mul_table_lle[256] = gf128mul_dat(xda_lle); -static const u16 gf128mul_table_bbe[256] = gf128mul_dat(xda_bbe); +static const u16 gf128mul_table_le[256] = gf128mul_dat(xda_le); +static const u16 gf128mul_table_be[256] = gf128mul_dat(xda_be); /* * The following functions multiply a field element by x or by x^8 in @@ -125,7 +140,7 @@ static void gf128mul_x_lle(be128 *r, const be128 *x) { u64 a = be64_to_cpu(x->a); u64 b = be64_to_cpu(x->b); - u64 _tt = gf128mul_table_lle[(b << 7) & 0xff]; + u64 _tt = gf128mul_table_le[(b << 7) & 0xff]; r->b = cpu_to_be64((b >> 1) | (a << 63)); r->a = cpu_to_be64((a >> 1) ^ (_tt << 48)); @@ -135,7 +150,7 @@ static void gf128mul_x_bbe(be128 *r, const be128 *x) { u64 a = be64_to_cpu(x->a); u64 b = be64_to_cpu(x->b); - u64 _tt = gf128mul_table_bbe[a >> 63]; + u64 _tt = gf128mul_table_be[a >> 63]; r->a = cpu_to_be64((a << 1) | (b >> 63)); r->b = cpu_to_be64((b << 1) ^ _tt); @@ -145,7 +160,7 @@ void gf128mul_x_ble(be128 *r, const be128 *x) { u64 a = le64_to_cpu(x->a); u64 b = le64_to_cpu(x->b); - u64 _tt = gf128mul_table_bbe[b >> 63]; + u64 _tt = gf128mul_table_be[b >> 63]; r->a = cpu_to_le64((a << 1) ^ _tt); r->b = cpu_to_le64((b << 1) | (a >> 63)); @@ -156,7 +171,7 @@ static void gf128mul_x8_lle(be128 *x) { u64 a = be64_to_cpu(x->a); u64 b = be64_to_cpu(x->b); - u64 _tt = gf128mul_table_lle[b & 0xff]; + u64 _tt = gf128mul_table_le[b & 0xff]; x->b = cpu_to_be64((b >> 8) | (a << 56)); x->a = cpu_to_be64((a >> 8) ^ (_tt << 48)); @@ -166,7 +181,7 @@ static void gf128mul_x8_bbe(be128 *x) { u64 a = be64_to_cpu(x->a); u64 b = be64_to_cpu(x->b); - u64 _tt = gf128mul_table_bbe[a >> 56]; + u64 _tt = gf128mul_table_be[a >> 56]; x->a = cpu_to_be64((a << 8) | (b >> 56)); x->b = cpu_to_be64((b << 8) ^ _tt); |
