HRSS: flatten sample distribution.

With HRSS-SXY, the sampling algorithm now longer has to be the same
between the two parties. Therefore we can change it at will (as long as
it remains reasonably uniform) and thus take the opportunity to make the
output distribution flatter.

Change-Id: I74c667fcf919fe11ddcf2f4fb8a540b5112268bf
Reviewed-on: https://boringssl-review.googlesource.com/c/34404
Commit-Queue: Adam Langley <agl@google.com>
Reviewed-by: David Benjamin <davidben@google.com>
diff --git a/crypto/hrss/hrss.c b/crypto/hrss/hrss.c
index 753d50d..d81a43f 100644
--- a/crypto/hrss/hrss.c
+++ b/crypto/hrss/hrss.c
@@ -1460,7 +1460,7 @@
   *words = word;
 }
 
-// mod3 treats |a| is a signed number and returns |a| mod 3.
+// mod3 treats |a| as a signed number and returns |a| mod 3.
 static uint16_t mod3(int16_t a) {
   const int16_t q = ((int32_t)a * 21845) >> 16;
   int16_t ret = a - 3 * q;
@@ -1794,69 +1794,21 @@
 // HRSS-specific functions
 // -----------------------
 
-// poly_short_sample implements the sampling algorithm given in [HRSSNIST]
-// section 1.8.1. The output coefficients are in {0, 1, 0xffff} which makes some
-// later computation easier.
+// poly_short_sample samples a vector of values in {0xffff (i.e. -1), 0, 1}.
+// This is the same action as the algorithm in [HRSSNIST] section 1.8.1, but
+// with HRSS-SXY the sampling algorithm is now a private detail of the
+// implementation (previously it had to match between two parties). This
+// function uses that freedom to implement a flatter distribution of values.
 static void poly_short_sample(struct poly *out,
                               const uint8_t in[HRSS_SAMPLE_BYTES]) {
-  // We wish to calculate the difference (mod 3) between two, two-bit numbers.
-  // Here is a table of results for a - b. Negative one is written as 0b11 so
-  // that a couple of shifts can be used to sign-extend it. Any input value of
-  // 0b11 is invalid and a convention is adopted that an invalid input results
-  // in an invalid output (0b10).
-  //
-  //  b  a result
-  // 00 00 00
-  // 00 01 01
-  // 00 10 11
-  // 00 11 10
-  // 01 00 11
-  // 01 01 00
-  // 01 10 01
-  // 01 11 10
-  // 10 00 01
-  // 10 01 11
-  // 10 10 00
-  // 10 11 10
-  // 11 00 10
-  // 11 01 10
-  // 11 10 10
-  // 11 11 10
-  //
-  // The result column is encoded in a single-word lookup-table:
-  // 0001 1110 1100 0110 0111 0010 1010 1010
-  //   1    d    c    6    7    2    a    a
-  static const uint32_t kLookup = 0x1dc672aa;
-
-  // In order to generate pairs of numbers mod 3 (non-uniformly) we treat pairs
-  // of bits in a uint32 as separate values and sum two random vectors of 1-bit
-  // numbers. This works because these pairs are isolated because no carry can
-  // spread between them.
-
-  uint16_t *p = out->v;
-  for (size_t i = 0; i < N / 8; i++) {
-    uint32_t v;
-    OPENSSL_memcpy(&v, in, sizeof(v));
-    in += sizeof(v);
-
-    uint32_t sums = (v & 0x55555555) + ((v >> 1) & 0x55555555);
-    for (unsigned j = 0; j < 8; j++) {
-      p[j] = (int32_t)(kLookup << ((sums & 15) << 1)) >> 30;
-      sums >>= 4;
-    }
-    p += 8;
+  OPENSSL_STATIC_ASSERT(HRSS_SAMPLE_BYTES == N - 1,
+                        "HRSS_SAMPLE_BYTES incorrect");
+  for (size_t i = 0; i < N - 1; i++) {
+    uint16_t v = mod3(in[i]);
+    // Map {0, 1, 2} -> {0, 1, 0xffff}
+    v |= ((v >> 1) ^ 1) - 1;
+    out->v[i] = v;
   }
-
-  // There are four values remaining.
-  uint16_t v;
-  OPENSSL_memcpy(&v, in, sizeof(v));
-
-  uint16_t sums = (v & 0x5555) + ((v >> 1) & 0x5555);
-  for (unsigned j = 0; j < 4; j++) {
-    p[j] = (int32_t)(kLookup << ((sums & 15) << 1)) >> 30;
-    sums >>= 4;
-  }
-
   out->v[N - 1] = 0;
 }
 
diff --git a/crypto/hrss/hrss_test.cc b/crypto/hrss/hrss_test.cc
index 97c1bf0..493255d 100644
--- a/crypto/hrss/hrss_test.cc
+++ b/crypto/hrss/hrss_test.cc
@@ -250,216 +250,217 @@
   HRSS_generate_key(&pub, &priv, generate_key_entropy);
 
   static const uint8_t kExpectedPub[HRSS_PUBLIC_KEY_BYTES] = {
-      0xf8, 0x9f, 0xa0, 0xfc, 0xf1, 0xd4, 0xfa, 0x4d, 0x8f, 0x35, 0x28, 0x73,
-      0x0e, 0x37, 0x18, 0x1d, 0x09, 0xf3, 0x9e, 0x16, 0x0d, 0x7f, 0x9c, 0x82,
-      0x17, 0xa1, 0xa1, 0x88, 0x6b, 0x29, 0x5b, 0x3a, 0x30, 0xcd, 0x6f, 0x8e,
-      0x0c, 0xd3, 0x38, 0x0c, 0x05, 0x68, 0x6e, 0x4c, 0xcc, 0x20, 0xd4, 0x06,
-      0x77, 0x0c, 0xac, 0x1c, 0x49, 0x14, 0x00, 0xd6, 0x9b, 0x1c, 0xde, 0x43,
-      0x0a, 0x59, 0x37, 0xd6, 0x46, 0x68, 0x1f, 0x04, 0xcb, 0x73, 0x92, 0x37,
-      0x2d, 0x7f, 0x57, 0x70, 0x16, 0xe8, 0x06, 0x48, 0x3b, 0x66, 0xb3, 0x63,
-      0x02, 0x5a, 0x71, 0x46, 0xdd, 0xa4, 0xee, 0xb8, 0x78, 0x44, 0xfd, 0x9e,
-      0xd0, 0x71, 0x16, 0x00, 0xbd, 0x01, 0x1e, 0x27, 0x2e, 0xa0, 0xc6, 0x8d,
-      0x55, 0x89, 0x7c, 0x2a, 0x01, 0x2b, 0x1b, 0x75, 0xa2, 0xc2, 0xd1, 0x5a,
-      0x67, 0xfa, 0xdd, 0x3b, 0x70, 0x9d, 0xdb, 0xcd, 0x73, 0x32, 0x5e, 0x24,
-      0xb1, 0xcf, 0x23, 0xbe, 0x3c, 0x56, 0xcc, 0xbe, 0x61, 0xdb, 0xe7, 0x3c,
-      0xc7, 0xf5, 0x09, 0xe6, 0x87, 0xa0, 0x09, 0x52, 0x9d, 0x61, 0x5b, 0xc6,
-      0xd4, 0xc5, 0x2e, 0xc2, 0x6c, 0x87, 0x30, 0x36, 0x49, 0x6f, 0x04, 0xaa,
-      0xb3, 0x26, 0xd5, 0x63, 0xcf, 0xd4, 0x74, 0x1e, 0xc7, 0x79, 0xb3, 0xfc,
-      0x8c, 0x41, 0x36, 0x79, 0xaa, 0xd5, 0xba, 0x64, 0x49, 0x48, 0xdb, 0xeb,
-      0xe8, 0x33, 0x7d, 0xbe, 0x3b, 0x67, 0xd7, 0xfd, 0x93, 0x1e, 0x80, 0x8d,
-      0x17, 0xab, 0x6f, 0xfd, 0x1c, 0x4b, 0x2d, 0x5b, 0x90, 0xf0, 0xf0, 0x5d,
-      0xbe, 0x8f, 0x81, 0x18, 0x29, 0x08, 0x9a, 0x47, 0x1b, 0xc2, 0x2d, 0xa2,
-      0x22, 0x5a, 0x4f, 0xe9, 0x81, 0x64, 0xdd, 0x53, 0x2e, 0x67, 0xe5, 0x07,
-      0x1a, 0xf0, 0x0c, 0x54, 0x9b, 0xe2, 0xf8, 0xe6, 0xb3, 0xb6, 0xe0, 0x5a,
-      0x74, 0xfa, 0x8d, 0x9c, 0xa5, 0x7c, 0x6e, 0x73, 0xba, 0xee, 0x6e, 0x6e,
-      0x31, 0xcb, 0x59, 0xd7, 0xfd, 0x94, 0x1c, 0x4d, 0x62, 0xc6, 0x87, 0x0b,
-      0x38, 0x54, 0xc6, 0x35, 0xac, 0xc8, 0x8c, 0xc0, 0xd9, 0x99, 0xee, 0xfc,
-      0xa9, 0xde, 0xc4, 0x50, 0x88, 0x8e, 0x24, 0xf6, 0xd6, 0x04, 0x54, 0x3e,
-      0x81, 0xc4, 0x96, 0x9a, 0x40, 0xe5, 0xef, 0x8b, 0xec, 0x41, 0x50, 0x1d,
-      0x14, 0xae, 0xa4, 0x5a, 0xac, 0xd4, 0x73, 0x31, 0xc3, 0x1d, 0xc1, 0x96,
-      0x89, 0xd8, 0x62, 0x97, 0x60, 0x3f, 0x58, 0x2a, 0x5f, 0xcf, 0xcb, 0x26,
-      0x99, 0x69, 0x81, 0x13, 0x9c, 0xaf, 0x17, 0x91, 0xa8, 0xeb, 0x9a, 0xf9,
-      0xd3, 0x83, 0x47, 0x66, 0xc7, 0xf8, 0xd8, 0xe3, 0xd2, 0x7e, 0x58, 0xa9,
-      0xf5, 0xb2, 0x03, 0xbe, 0x7e, 0xa5, 0x29, 0x9d, 0xff, 0xd1, 0xd8, 0x55,
-      0x39, 0xc7, 0x2c, 0xce, 0x03, 0x64, 0xdc, 0x18, 0xe7, 0xb0, 0x60, 0x46,
-      0x26, 0xeb, 0xb7, 0x61, 0x4b, 0x91, 0x2c, 0xd8, 0xa2, 0xee, 0x63, 0x2e,
-      0x15, 0x0a, 0x58, 0x88, 0x04, 0xb1, 0xed, 0x6d, 0xf1, 0x5c, 0xc7, 0xee,
-      0x60, 0x38, 0x26, 0xc9, 0x31, 0x7e, 0x69, 0xe4, 0xac, 0x3c, 0x72, 0x09,
-      0x3e, 0xe6, 0x24, 0x30, 0x44, 0x6e, 0x66, 0x83, 0xb9, 0x2a, 0x22, 0xaf,
-      0x26, 0x1e, 0xaa, 0xa3, 0xf4, 0xb1, 0xa1, 0x5c, 0xfa, 0x5f, 0x0d, 0x71,
-      0xac, 0xe3, 0xe0, 0xc3, 0xdd, 0x4f, 0x96, 0x57, 0x8b, 0x58, 0xac, 0xe3,
-      0x42, 0x8e, 0x47, 0x72, 0xb1, 0xe4, 0x19, 0x68, 0x3e, 0xbb, 0x19, 0x14,
-      0xdf, 0x16, 0xb5, 0xde, 0x7f, 0x37, 0xaf, 0xd8, 0xd3, 0x3d, 0x6a, 0x16,
-      0x1b, 0x26, 0xd3, 0xcc, 0x53, 0x82, 0x57, 0x90, 0x89, 0xc5, 0x7e, 0x6d,
-      0x7e, 0x99, 0x5b, 0xcd, 0xd3, 0x18, 0xbb, 0x89, 0xef, 0x76, 0xbd, 0xd2,
-      0x62, 0xf0, 0xe8, 0x25, 0x2a, 0x8d, 0xe2, 0x21, 0xea, 0xde, 0x6e, 0xa5,
-      0xa4, 0x3d, 0x58, 0xee, 0xdf, 0x90, 0xc1, 0xa1, 0x38, 0x5d, 0x11, 0x50,
-      0xb5, 0xac, 0x9d, 0xb4, 0xfd, 0xef, 0x53, 0xe8, 0xc0, 0x17, 0x6c, 0x4f,
-      0x31, 0xe0, 0xcc, 0x8f, 0x80, 0x7a, 0x84, 0x14, 0xde, 0xee, 0xec, 0xdd,
-      0x6a, 0xad, 0x29, 0x65, 0xa5, 0x72, 0xc3, 0x73, 0x5f, 0xe3, 0x6f, 0x60,
-      0xb1, 0xfb, 0x0f, 0xaa, 0xc6, 0xda, 0x53, 0x4a, 0xb1, 0x92, 0x2a, 0xb7,
-      0x02, 0xbe, 0xf9, 0xdf, 0x37, 0x16, 0xe7, 0x5c, 0x38, 0x0b, 0x3c, 0xe2,
-      0xdd, 0x90, 0xb8, 0x7b, 0x48, 0x69, 0x79, 0x81, 0xc5, 0xae, 0x9a, 0x0d,
-      0x78, 0x95, 0x52, 0x63, 0x80, 0xda, 0x46, 0x69, 0x20, 0x57, 0x9b, 0x27,
-      0xe2, 0xe8, 0xbd, 0x2f, 0x45, 0xe6, 0x46, 0x40, 0xae, 0x50, 0xd5, 0xa2,
-      0x53, 0x93, 0xe1, 0x99, 0xfd, 0x13, 0x7c, 0xf6, 0x22, 0xc4, 0x6c, 0xab,
-      0xe3, 0xc9, 0x55, 0x0a, 0x16, 0x67, 0x68, 0x26, 0x6b, 0xd6, 0x7d, 0xde,
-      0xd3, 0xae, 0x71, 0x32, 0x02, 0xf1, 0x27, 0x67, 0x47, 0x74, 0xd9, 0x40,
-      0x35, 0x1d, 0x25, 0x72, 0x32, 0xdf, 0x75, 0xd5, 0x60, 0x26, 0xab, 0x90,
-      0xfa, 0xeb, 0x26, 0x11, 0x4b, 0xb4, 0xc5, 0xc2, 0x3e, 0xa9, 0x23, 0x3a,
-      0x4e, 0x6a, 0xb1, 0xbb, 0xb3, 0xea, 0xf9, 0x1e, 0xe4, 0x10, 0xf5, 0xdc,
-      0x35, 0xde, 0xb5, 0xee, 0xf0, 0xde, 0xa1, 0x18, 0x80, 0xc7, 0x13, 0x68,
-      0x46, 0x94, 0x0e, 0x2a, 0x8e, 0xf8, 0xe9, 0x26, 0x84, 0x42, 0x0f, 0x56,
-      0xed, 0x67, 0x7f, 0xeb, 0x7d, 0x35, 0x07, 0x01, 0x11, 0x81, 0x8b, 0x56,
-      0x88, 0xc6, 0x58, 0x61, 0x65, 0x3c, 0x5d, 0x9c, 0x58, 0x25, 0xd6, 0xdf,
-      0x4e, 0x3b, 0x93, 0xbf, 0x82, 0xe1, 0x19, 0xb8, 0xda, 0xde, 0x26, 0x38,
-      0xf2, 0xd9, 0x95, 0x24, 0x98, 0xde, 0x58, 0xf7, 0x0c, 0xe9, 0x32, 0xbb,
-      0xcc, 0xf7, 0x92, 0x69, 0xa2, 0xf0, 0xc3, 0xfa, 0xd2, 0x31, 0x8b, 0x43,
-      0x4e, 0x03, 0xe2, 0x13, 0x79, 0x6e, 0x73, 0x63, 0x3b, 0x45, 0xde, 0x80,
-      0xf4, 0x26, 0xb1, 0x38, 0xed, 0x62, 0x55, 0xc6, 0x6a, 0x67, 0x00, 0x2d,
-      0xba, 0xb2, 0xc5, 0xb6, 0x97, 0x62, 0x28, 0x64, 0x30, 0xb9, 0xfb, 0x3f,
-      0x94, 0x03, 0x48, 0x36, 0x2c, 0x5d, 0xfd, 0x08, 0x96, 0x40, 0xd1, 0x6c,
-      0xe5, 0xd0, 0xf8, 0x99, 0x40, 0x82, 0x87, 0xd7, 0xdc, 0x2f, 0x8b, 0xaa,
-      0x31, 0x96, 0x0a, 0x34, 0x33, 0xa6, 0xf1, 0x84, 0x6e, 0x33, 0x73, 0xc5,
-      0xe3, 0x26, 0xad, 0xd0, 0xcb, 0x62, 0x71, 0x82, 0xab, 0xd1, 0x82, 0x33,
-      0xe6, 0xca, 0xd0, 0x3e, 0xf5, 0x4d, 0x12, 0x6e, 0xf1, 0x83, 0xbd, 0xdc,
-      0x4d, 0xdf, 0x49, 0xbc, 0x63, 0xae, 0x7e, 0x59, 0xe8, 0x3c, 0x0d, 0xd6,
-      0x1d, 0x41, 0x89, 0x72, 0x52, 0xc0, 0xae, 0xd1, 0x2f, 0x0a, 0x8a, 0xce,
-      0x26, 0xd0, 0x3e, 0x0c, 0x71, 0x32, 0x52, 0xb2, 0xe4, 0xee, 0xa2, 0xe5,
-      0x28, 0xb6, 0x33, 0x69, 0x97, 0x5a, 0x53, 0xdb, 0x56, 0x63, 0xe9, 0xb3,
-      0x6d, 0x60, 0xf4, 0x7a, 0xce, 0xec, 0x36, 0x65, 0xd5, 0xca, 0x63, 0x2a,
-      0x19, 0x90, 0x14, 0x7b, 0x02, 0x33, 0xfa, 0x11, 0x58, 0x5a, 0xd9, 0xc5,
-      0x54, 0xf3, 0x28, 0xd5, 0x6e, 0xea, 0x85, 0xf5, 0x09, 0xbb, 0x81, 0x44,
-      0x1c, 0x63, 0x66, 0x81, 0xc5, 0x96, 0x2d, 0x7c, 0x0e, 0x75, 0x7b, 0xb4,
-      0x7e, 0x4e, 0x0c, 0xfd, 0x3c, 0xc5, 0x5a, 0x22, 0x85, 0x5c, 0xc8, 0xf3,
-      0x97, 0x98, 0x2c, 0xe9, 0x46, 0xb4, 0x02, 0xcf, 0x7d, 0xa4, 0xf2, 0x44,
-      0x7a, 0x89, 0x71, 0xa0, 0xfa, 0xb6, 0xa3, 0xaf, 0x13, 0x25, 0x46, 0xe2,
-      0x64, 0xe3, 0x69, 0xba, 0xf9, 0x68, 0x5c, 0xc0, 0xb7, 0xa8, 0xa6, 0x4b,
-      0xe1, 0x42, 0xe9, 0xb5, 0xc7, 0x84, 0xbb, 0xa6, 0x4b, 0x10, 0x4e, 0xd4,
-      0x68, 0x70, 0x0a, 0x75, 0x2a, 0xbb, 0x9d, 0xa0, 0xcb, 0xf0, 0x36, 0x4c,
-      0x70, 0x6c, 0x60, 0x4d, 0xfe, 0xe8, 0xc8, 0x66, 0x80, 0x1b, 0xf7, 0xcc,
-      0x1a, 0xdd, 0x6b, 0xa7, 0xa7, 0x25, 0x61, 0x0c, 0x31, 0xf0, 0x34, 0x63,
-      0x00, 0x0e, 0x48, 0x6a, 0x5a, 0x8d, 0x47, 0x94, 0x3f, 0x14, 0x16, 0xa8,
-      0x8a, 0x49, 0xbb, 0x0c, 0x43, 0x21, 0xda, 0xf2, 0xc5, 0xd0, 0xff, 0x19,
-      0x3e, 0x36, 0x64, 0x20, 0xb3, 0x70, 0xae, 0x54, 0xca, 0x73, 0x05, 0x56,
-      0x7a, 0x49, 0x45, 0xe9, 0x46, 0xbc, 0xc2, 0x61, 0x70, 0x40, 0x7c, 0xb0,
-      0xf7, 0xea, 0xc0, 0xd1, 0xb0, 0x77, 0x2c, 0xc7, 0xdd, 0x88, 0xcb, 0x9d,
-      0xea, 0x55, 0x6c, 0x5c, 0x28, 0xb8, 0x84, 0x1c, 0x2c, 0x06,
+      0x4a, 0x21, 0x39, 0x7c, 0xb4, 0xa6, 0x58, 0x15, 0x35, 0x77, 0xe4, 0x2a,
+      0x02, 0x79, 0xc0, 0x02, 0xe2, 0x21, 0x27, 0x5f, 0x49, 0xc7, 0x2c, 0x14,
+      0xb6, 0xe0, 0x67, 0xc2, 0xc7, 0x09, 0x62, 0x0c, 0xe5, 0x23, 0x9c, 0x40,
+      0xd7, 0x7e, 0xf5, 0x55, 0x5a, 0xa2, 0xd0, 0x9f, 0xd3, 0x8c, 0x67, 0x7b,
+      0x48, 0xa4, 0x53, 0x8d, 0x39, 0xb1, 0xcc, 0x99, 0x29, 0xf7, 0x83, 0xbf,
+      0x6f, 0x9b, 0x16, 0x73, 0x23, 0xcc, 0xc3, 0x86, 0x98, 0xb1, 0x7c, 0x53,
+      0xb1, 0xf5, 0xf4, 0xdd, 0xc8, 0x97, 0x5e, 0xd3, 0x6d, 0x63, 0xce, 0xf3,
+      0xa2, 0xf6, 0xef, 0x94, 0xed, 0x4a, 0x3e, 0xe6, 0x4b, 0xa2, 0xfb, 0x87,
+      0xa3, 0xbc, 0x65, 0x1c, 0x17, 0x64, 0x25, 0xa7, 0xb4, 0xa1, 0xe6, 0x84,
+      0x06, 0x72, 0x0c, 0x28, 0xe8, 0xfc, 0xaa, 0xca, 0xf8, 0x20, 0x79, 0x89,
+      0xa9, 0xf0, 0x60, 0xdf, 0xd6, 0xd4, 0xe0, 0xaf, 0x99, 0x54, 0x21, 0xaf,
+      0x76, 0xd5, 0x9a, 0x31, 0x80, 0xea, 0x7f, 0x03, 0x6c, 0x14, 0x74, 0x06,
+      0x9c, 0x93, 0xe3, 0x93, 0xcc, 0x46, 0x4d, 0x82, 0xda, 0xdf, 0x67, 0xe9,
+      0x6d, 0x58, 0x2b, 0x49, 0xf3, 0x10, 0x71, 0xa0, 0xc5, 0xec, 0xa0, 0x29,
+      0xd7, 0x7c, 0x43, 0xd5, 0x05, 0x7e, 0x14, 0x8c, 0x39, 0x28, 0xf9, 0x46,
+      0x3d, 0xc1, 0x10, 0x6c, 0x2f, 0xaa, 0xca, 0x11, 0x87, 0x6a, 0xe2, 0xb1,
+      0xf6, 0x31, 0x76, 0xb0, 0xdc, 0x30, 0x8a, 0x97, 0x7d, 0xdc, 0xe4, 0xd1,
+      0x18, 0xe9, 0x03, 0x91, 0xf5, 0xd2, 0x94, 0x4d, 0x71, 0xf7, 0x35, 0xc8,
+      0x3e, 0x46, 0xaf, 0xa3, 0xeb, 0x35, 0x07, 0x01, 0x77, 0xc5, 0x58, 0xca,
+      0x82, 0x67, 0x3e, 0x4f, 0x01, 0x88, 0xa4, 0xa0, 0xea, 0x0a, 0xb7, 0x13,
+      0x06, 0xbe, 0xb6, 0x61, 0xa4, 0xa2, 0x28, 0xe2, 0x32, 0xcf, 0x25, 0x46,
+      0xcf, 0xce, 0xf5, 0x57, 0x9b, 0x74, 0x8f, 0xfd, 0xbc, 0xfa, 0x3a, 0xa2,
+      0x18, 0x22, 0xf1, 0xb1, 0x43, 0x12, 0xe8, 0xe2, 0xe3, 0x06, 0xe6, 0x1c,
+      0xa7, 0x76, 0x2d, 0x0d, 0xe5, 0x5f, 0xbd, 0x8f, 0xa0, 0x95, 0xcd, 0xe9,
+      0x28, 0xdb, 0xcc, 0xe5, 0x66, 0x33, 0xd4, 0x4b, 0xf9, 0x0c, 0x42, 0x9b,
+      0x27, 0xee, 0x11, 0xd0, 0xe3, 0x0b, 0x9d, 0xce, 0x2c, 0x91, 0x7a, 0x0e,
+      0xb8, 0xde, 0x31, 0x73, 0x86, 0x8e, 0x34, 0x59, 0x93, 0x2e, 0x37, 0x9d,
+      0xc2, 0x3e, 0x89, 0x0b, 0x47, 0xff, 0xa6, 0x55, 0x21, 0xe6, 0x4f, 0x72,
+      0x7c, 0xcc, 0xe5, 0xb8, 0x18, 0x2c, 0x10, 0xcb, 0xce, 0x48, 0xa5, 0xc5,
+      0x26, 0xb6, 0x19, 0x76, 0xc5, 0x38, 0xf0, 0x38, 0x72, 0xec, 0x22, 0xf9,
+      0x25, 0xde, 0x1c, 0x0c, 0x1b, 0x3e, 0x43, 0xc5, 0x5c, 0x8c, 0xdb, 0xf1,
+      0x42, 0x66, 0xbc, 0xdf, 0xa0, 0x82, 0x4b, 0xec, 0xe1, 0x50, 0x42, 0x57,
+      0x84, 0x60, 0xfd, 0x89, 0x12, 0x1b, 0xf6, 0xf9, 0x4d, 0x0d, 0x16, 0xe8,
+      0xa4, 0xe2, 0x67, 0x2c, 0x8f, 0x22, 0xea, 0xba, 0x46, 0x34, 0xce, 0x97,
+      0x8b, 0x4c, 0x38, 0x0e, 0x16, 0x82, 0xb6, 0xf3, 0x34, 0x38, 0x07, 0x87,
+      0x73, 0x2a, 0x3d, 0x80, 0x56, 0x4b, 0x85, 0x67, 0xca, 0x2a, 0x19, 0xb6,
+      0xb6, 0x2c, 0xfe, 0xd8, 0x02, 0xe5, 0xad, 0xd0, 0x61, 0x79, 0x73, 0xab,
+      0xda, 0x3b, 0xa4, 0x51, 0xb3, 0xf7, 0x85, 0x99, 0xb2, 0xd0, 0x64, 0x97,
+      0xb7, 0x3c, 0x0e, 0x58, 0xdf, 0xd2, 0x98, 0x98, 0x18, 0x1a, 0xf5, 0x59,
+      0xcd, 0xc5, 0x48, 0x17, 0x10, 0x9f, 0xd8, 0x19, 0xbd, 0xd0, 0x42, 0x71,
+      0x1c, 0x30, 0xc6, 0x76, 0xe9, 0xb0, 0xee, 0xf5, 0x38, 0x05, 0xbe, 0x9b,
+      0x6c, 0x0d, 0xb0, 0xd0, 0xda, 0x1c, 0x89, 0xbd, 0x40, 0x5d, 0xc2, 0x5a,
+      0xbe, 0x83, 0xa6, 0xb5, 0x47, 0xa7, 0xf8, 0xb9, 0xbf, 0xa2, 0x65, 0x17,
+      0x1e, 0xd8, 0x28, 0x42, 0xbe, 0xb0, 0x35, 0xf6, 0x7b, 0x88, 0x38, 0xbe,
+      0xf5, 0xb5, 0x1b, 0x63, 0x7a, 0x83, 0x92, 0x0d, 0x64, 0xad, 0x92, 0x59,
+      0x97, 0x55, 0x5c, 0x60, 0xab, 0x48, 0x8e, 0x23, 0x27, 0x22, 0x75, 0x3b,
+      0x7c, 0x9c, 0x69, 0x13, 0x52, 0x6b, 0xae, 0xfd, 0x38, 0xe5, 0x4b, 0x36,
+      0x78, 0x55, 0x92, 0xb5, 0x8f, 0x25, 0xde, 0x0e, 0x93, 0xe3, 0x1d, 0x83,
+      0x62, 0x05, 0x6a, 0x5a, 0xff, 0x7f, 0x77, 0xf7, 0x1b, 0xfc, 0x21, 0x45,
+      0xf7, 0xb8, 0xfa, 0xcb, 0x00, 0x5e, 0x85, 0xf9, 0x2f, 0x15, 0x2f, 0xcf,
+      0x17, 0x9e, 0x84, 0xf6, 0xf5, 0x15, 0x6e, 0xdd, 0xb4, 0x73, 0x44, 0xc2,
+      0x2c, 0x74, 0xae, 0x27, 0x5f, 0x19, 0xe7, 0x51, 0x61, 0xc1, 0x82, 0xce,
+      0xf1, 0x5b, 0xa0, 0x6f, 0x0b, 0x13, 0x10, 0x68, 0xb7, 0xee, 0xfb, 0x8a,
+      0x85, 0xe2, 0xd6, 0x17, 0x55, 0x26, 0xa5, 0xc5, 0xb3, 0x94, 0x45, 0xdf,
+      0x49, 0xe6, 0x50, 0xf8, 0x99, 0xd8, 0x3c, 0xcb, 0x94, 0x80, 0x67, 0x3b,
+      0x73, 0xac, 0xf6, 0x46, 0x31, 0x63, 0xb3, 0x1b, 0x47, 0xce, 0x40, 0x3f,
+      0x8c, 0xd0, 0x82, 0xc4, 0x79, 0x3a, 0x7c, 0x48, 0x10, 0xe3, 0x97, 0x98,
+      0xdc, 0x0b, 0x62, 0x42, 0xfa, 0x26, 0x05, 0xf6, 0x8c, 0x32, 0xa9, 0xb6,
+      0x2c, 0x4f, 0x85, 0xd2, 0x9b, 0xf3, 0x89, 0x1f, 0x91, 0xca, 0x12, 0x3d,
+      0xe2, 0xa8, 0x0b, 0xca, 0x64, 0x28, 0x0e, 0xa7, 0xfd, 0xd8, 0xa3, 0xcb,
+      0x0a, 0xd9, 0x97, 0x2d, 0xc3, 0xf2, 0x39, 0x74, 0xdb, 0xe3, 0x9a, 0x87,
+      0x1a, 0xe0, 0x33, 0xe3, 0x92, 0xe8, 0xde, 0xb5, 0x08, 0x28, 0xcb, 0xd7,
+      0xb6, 0x79, 0xec, 0x71, 0xcc, 0xe5, 0xd1, 0x4b, 0x89, 0x96, 0x5f, 0xfa,
+      0xfd, 0x4b, 0xd0, 0xa8, 0x66, 0x0d, 0xb4, 0xa7, 0x51, 0x56, 0xbc, 0xa7,
+      0x74, 0x07, 0x7f, 0xae, 0x0e, 0xf6, 0x9c, 0x13, 0xd9, 0xf2, 0xed, 0x12,
+      0xa9, 0x87, 0x3e, 0xb7, 0x9d, 0x53, 0x8a, 0x82, 0x2d, 0x03, 0x2f, 0xac,
+      0x94, 0x84, 0x95, 0x00, 0x29, 0x09, 0x01, 0x38, 0x62, 0xff, 0xaf, 0xfd,
+      0x10, 0x2b, 0x31, 0x03, 0xb2, 0x4f, 0x51, 0xfb, 0x76, 0x27, 0x1e, 0x25,
+      0x82, 0x79, 0x65, 0x69, 0xfa, 0x24, 0xaf, 0xcb, 0xe8, 0x40, 0x8d, 0x7d,
+      0xd2, 0x9a, 0x12, 0x69, 0x2f, 0xe4, 0xce, 0x99, 0x98, 0x4f, 0x6c, 0x46,
+      0xfd, 0x63, 0x40, 0x50, 0xef, 0x22, 0x02, 0x68, 0x2e, 0x53, 0xbb, 0x00,
+      0xa3, 0x65, 0x61, 0x3e, 0x97, 0xd4, 0x5f, 0xa2, 0xc1, 0x66, 0xcd, 0x04,
+      0xdc, 0xda, 0x55, 0x10, 0x28, 0x0d, 0x40, 0x11, 0xe6, 0x68, 0xed, 0x68,
+      0x38, 0x7d, 0x20, 0xc3, 0x97, 0x9d, 0xcb, 0x6e, 0x30, 0xfc, 0xbe, 0x63,
+      0xe7, 0x72, 0x47, 0x05, 0xf5, 0x0b, 0x7e, 0x66, 0x3b, 0xc5, 0x3a, 0x85,
+      0x5a, 0xa3, 0xc5, 0x72, 0x9d, 0xb9, 0xc1, 0xb4, 0x80, 0x98, 0x6e, 0x40,
+      0x86, 0xc9, 0xcb, 0xa3, 0xab, 0x77, 0xc2, 0x56, 0xfc, 0xcb, 0x6e, 0x12,
+      0xf5, 0x63, 0x62, 0xf8, 0xff, 0x91, 0x15, 0xa7, 0xa1, 0x5e, 0xb6, 0xee,
+      0x69, 0x4d, 0x5b, 0x5f, 0x4e, 0xfa, 0xd3, 0x61, 0xca, 0xec, 0x14, 0xfd,
+      0xd9, 0x10, 0xf5, 0x4a, 0x05, 0x5f, 0x29, 0xcb, 0x77, 0x2c, 0x2d, 0xe2,
+      0x90, 0x67, 0x62, 0x78, 0x75, 0xa9, 0x4e, 0x20, 0x00, 0x0c, 0x91, 0x84,
+      0xba, 0xed, 0x1c, 0xce, 0xbd, 0x57, 0x4f, 0xa5, 0x2f, 0x59, 0x6c, 0x4c,
+      0xdf, 0x5f, 0xaa, 0x32, 0xf0, 0x86, 0x09, 0x15, 0x36, 0xc6, 0xe6, 0x6a,
+      0x24, 0xb4, 0xb3, 0x09, 0xdd, 0x32, 0xc5, 0x95, 0xac, 0x60, 0xb5, 0x09,
+      0x97, 0x36, 0xa1, 0x3c, 0x8f, 0x0e, 0x90, 0x8e, 0xcd, 0xd0, 0x49, 0x75,
+      0xf7, 0xf3, 0x80, 0x80, 0xcb, 0x1f, 0xee, 0xf2, 0x6a, 0x2f, 0x19, 0x8c,
+      0xba, 0x10, 0x00, 0xda, 0x13, 0xef, 0x10, 0x2b, 0xb7, 0xef, 0xfd, 0xd1,
+      0xe0, 0x7c, 0xf8, 0x46, 0x01, 0x69, 0x9b, 0x99, 0x80, 0x51, 0x1f, 0x74,
+      0x3b, 0x67, 0x93, 0x18, 0x5e, 0xd4, 0x34, 0x6c, 0x81, 0x76, 0x02, 0xef,
+      0x91, 0xa4, 0x22, 0x2a, 0x23, 0x1b, 0x58, 0x43, 0x75, 0x65, 0x13, 0x87,
+      0x98, 0x60, 0x14, 0x25, 0x28, 0x67, 0xa3, 0x34, 0x8c, 0xe0, 0xd5, 0xd3,
+      0x51, 0x33, 0x68, 0xff, 0x65, 0x59, 0x5a, 0xa7, 0xb2, 0x6b, 0x01, 0xad,
+      0x70, 0x06, 0x73, 0x01, 0x51, 0x1b, 0xe1, 0xec, 0x28, 0x2f, 0x8a, 0x85,
+      0x5a, 0x10, 0xd0, 0x0e, 0x6b, 0x35, 0x45, 0x2e, 0x61, 0xdd, 0x77, 0x20,
+      0xb1, 0x35, 0x3b, 0xa8, 0xdd, 0x8a, 0xe2, 0x15, 0x79, 0x07,
   };
   uint8_t pub_bytes[HRSS_PUBLIC_KEY_BYTES];
   HRSS_marshal_public_key(pub_bytes, &pub);
   EXPECT_EQ(Bytes(pub_bytes), Bytes(kExpectedPub));
 
+  uint8_t encap_entropy[HRSS_ENCAP_BYTES];
+  for (size_t i = 0; i < sizeof(encap_entropy); i++) {
+    encap_entropy[i] = 31 + i;
+  }
   uint8_t ciphertext[HRSS_CIPHERTEXT_BYTES];
   uint8_t shared_key[HRSS_KEY_BYTES];
-  OPENSSL_STATIC_ASSERT(
-      sizeof(kExpectedPub) >= HRSS_ENCAP_BYTES,
-      "Private key too small to use as input to HRSS encapsulation");
-  HRSS_encap(ciphertext, shared_key, &pub, kExpectedPub);
+  HRSS_encap(ciphertext, shared_key, &pub, encap_entropy);
 
   static const uint8_t kExpectedCiphertext[HRSS_CIPHERTEXT_BYTES] = {
-      0x8e, 0x6b, 0x46, 0x9d, 0x4a, 0xef, 0xa6, 0x8c, 0x28, 0x7b, 0xec, 0x6f,
-      0x13, 0x2d, 0x7f, 0x6c, 0xca, 0x7d, 0x9e, 0x6b, 0x54, 0x62, 0xa3, 0x13,
-      0xe1, 0x1e, 0x8f, 0x5f, 0x71, 0x67, 0xc4, 0x85, 0xdf, 0xd5, 0x6b, 0xbd,
-      0x86, 0x0f, 0x98, 0xec, 0xa5, 0x04, 0xf7, 0x7b, 0x2a, 0xbe, 0xcb, 0xac,
-      0x29, 0xbe, 0xe1, 0x0f, 0xbc, 0x62, 0x87, 0x85, 0x7f, 0x05, 0xae, 0xe4,
-      0x3f, 0x87, 0xfc, 0x1f, 0xf7, 0x45, 0x1e, 0xa3, 0xdb, 0xb1, 0xa0, 0x25,
-      0xba, 0x82, 0xec, 0xca, 0x8d, 0xab, 0x7a, 0x20, 0x03, 0xeb, 0xe5, 0x5c,
-      0x9f, 0xd0, 0x46, 0x78, 0xf1, 0x5a, 0xc7, 0x9e, 0xb4, 0x10, 0x6d, 0x37,
-      0xc0, 0x75, 0x08, 0xfb, 0xeb, 0xcb, 0xd8, 0x35, 0x21, 0x9b, 0x89, 0xa0,
-      0xaa, 0x87, 0x00, 0x66, 0x38, 0x37, 0x68, 0xa4, 0xa3, 0x93, 0x8e, 0x2b,
-      0xca, 0xf7, 0x7a, 0x43, 0xb2, 0x15, 0x79, 0x81, 0xce, 0xa9, 0x09, 0xcb,
-      0x29, 0xd4, 0xcc, 0xef, 0xf1, 0x9b, 0xbd, 0xe6, 0x63, 0xd5, 0x26, 0x0f,
-      0xe8, 0x8b, 0xdf, 0xf1, 0xc3, 0xb4, 0x18, 0x0e, 0xf2, 0x1d, 0x5d, 0x82,
-      0x9b, 0x1f, 0xf3, 0xca, 0x36, 0x2a, 0x26, 0x0a, 0x7f, 0xc4, 0x0d, 0xbd,
-      0x5b, 0x15, 0x1c, 0x18, 0x6c, 0x11, 0x4e, 0xec, 0x36, 0x01, 0xc1, 0x15,
-      0xab, 0xf7, 0x0b, 0x1a, 0xd3, 0xa1, 0xbd, 0x68, 0xc8, 0x59, 0xe7, 0x49,
-      0x5c, 0xd5, 0x4b, 0x8c, 0x31, 0xdb, 0xb3, 0xea, 0x88, 0x09, 0x2f, 0xb9,
-      0x8b, 0xfd, 0x96, 0x35, 0x88, 0x53, 0x72, 0x40, 0xcd, 0x89, 0x75, 0xb4,
-      0x20, 0xf6, 0xf6, 0xe5, 0x74, 0x19, 0x48, 0xaf, 0x4b, 0xaa, 0x42, 0xa4,
-      0xc8, 0x90, 0xee, 0xf3, 0x12, 0x04, 0x63, 0x90, 0x92, 0x8a, 0x89, 0xc3,
-      0xa0, 0x7e, 0xfe, 0x19, 0xb3, 0x54, 0x53, 0x83, 0xe9, 0xc1, 0x6c, 0xe3,
-      0x97, 0xa6, 0x27, 0xc3, 0x20, 0x9a, 0x79, 0x35, 0xc9, 0xb5, 0xc0, 0x90,
-      0xe1, 0x56, 0x84, 0x69, 0xc2, 0x54, 0x77, 0x52, 0x48, 0x55, 0x71, 0x3e,
-      0xcd, 0xa7, 0xd6, 0x25, 0x5d, 0x49, 0x13, 0xd2, 0x59, 0xd7, 0xe1, 0xd1,
-      0x70, 0x46, 0xa0, 0xd4, 0xee, 0x59, 0x13, 0x1f, 0x1a, 0xd3, 0x39, 0x7d,
-      0xb0, 0x79, 0xf7, 0xc0, 0x73, 0x5e, 0xbb, 0x08, 0xf7, 0x5c, 0xb0, 0x31,
-      0x41, 0x3d, 0x7b, 0x1e, 0xf0, 0xe6, 0x47, 0x5c, 0x37, 0xd5, 0x54, 0xf1,
-      0xbb, 0x64, 0xd7, 0x41, 0x8b, 0x34, 0x55, 0xaa, 0xc3, 0x5a, 0x9c, 0xa0,
-      0xcc, 0x29, 0x8e, 0x5a, 0x1a, 0x93, 0x5a, 0x49, 0xd3, 0xd0, 0xa0, 0x56,
-      0xda, 0x32, 0xa2, 0xa9, 0xa7, 0x13, 0x42, 0x93, 0x9b, 0x20, 0x32, 0x37,
-      0x5c, 0x3e, 0x03, 0xa5, 0x28, 0x10, 0x93, 0xdd, 0xa0, 0x04, 0x7b, 0x2a,
-      0xbd, 0x31, 0xc3, 0x6a, 0x89, 0x58, 0x6e, 0x55, 0x0e, 0xc9, 0x5c, 0x70,
-      0x07, 0x10, 0xf1, 0x9a, 0xbd, 0xfb, 0xd2, 0xb7, 0x94, 0x5b, 0x4f, 0x8d,
-      0x90, 0xfa, 0xee, 0xae, 0x37, 0x48, 0xc5, 0xf8, 0x16, 0xa1, 0x3b, 0x70,
-      0x03, 0x1f, 0x0e, 0xb8, 0xbd, 0x8d, 0x30, 0x4f, 0x95, 0x31, 0x0b, 0x9f,
-      0xfc, 0x80, 0xf8, 0xef, 0xa3, 0x3c, 0xbc, 0xe2, 0x23, 0x23, 0x3e, 0x2a,
-      0x55, 0x11, 0xe8, 0x2c, 0x17, 0xea, 0x1c, 0xbd, 0x1d, 0x2d, 0x1b, 0xd5,
-      0x16, 0x9e, 0x05, 0xfc, 0x89, 0x64, 0x50, 0x4d, 0x9a, 0x22, 0x50, 0xc6,
-      0x5a, 0xd9, 0x58, 0x99, 0x8f, 0xbd, 0xf2, 0x4f, 0x2c, 0xdb, 0x51, 0x6a,
-      0x86, 0xe2, 0xc6, 0x64, 0x8f, 0x54, 0x1a, 0xf2, 0xcb, 0x34, 0x88, 0x08,
-      0xbd, 0x2a, 0x8f, 0xec, 0x29, 0xf5, 0x22, 0x36, 0x83, 0x99, 0xb9, 0x71,
-      0x8c, 0x99, 0x5c, 0xec, 0x91, 0x78, 0xc1, 0xe2, 0x2d, 0xe9, 0xd1, 0x4d,
-      0xf5, 0x15, 0x93, 0x4d, 0x93, 0x92, 0x9f, 0x0f, 0x33, 0x5e, 0xcd, 0x58,
-      0x5f, 0x3d, 0x52, 0xb9, 0x38, 0x6a, 0x85, 0x63, 0x8b, 0x63, 0x29, 0xcb,
-      0x67, 0x12, 0x25, 0xc2, 0x44, 0xd7, 0xab, 0x1a, 0x24, 0xca, 0x3d, 0xca,
-      0x77, 0xce, 0x28, 0x68, 0x1a, 0x91, 0xed, 0x7b, 0xc9, 0x70, 0x84, 0xab,
-      0xe2, 0xd4, 0xf4, 0xac, 0x58, 0xf6, 0x70, 0x99, 0xfc, 0x99, 0x4d, 0xbd,
-      0xb4, 0x1b, 0x4f, 0x15, 0x86, 0x95, 0x08, 0xd1, 0x4e, 0x73, 0xa9, 0xbc,
-      0x6a, 0x8c, 0xbc, 0xb5, 0x4b, 0xe0, 0xee, 0x35, 0x24, 0xf9, 0x12, 0xf5,
-      0x88, 0x70, 0x50, 0x6c, 0xfe, 0x0d, 0x35, 0xbd, 0xf7, 0xc4, 0x2e, 0x39,
-      0x16, 0x30, 0x6c, 0xf3, 0xb2, 0x19, 0x44, 0xaa, 0xcb, 0x4a, 0xf6, 0x75,
-      0xb7, 0x09, 0xb9, 0xe1, 0x47, 0x71, 0x70, 0x5c, 0x05, 0x5f, 0x50, 0x50,
-      0x9c, 0xd0, 0xe3, 0xc7, 0x91, 0xee, 0x6b, 0xc7, 0x0f, 0x71, 0x1b, 0xc3,
-      0x48, 0x8b, 0xed, 0x15, 0x26, 0x8c, 0xc3, 0xd5, 0x54, 0x08, 0xcc, 0x33,
-      0x79, 0xc0, 0x9f, 0x49, 0xc8, 0x75, 0xef, 0xb6, 0xf3, 0x29, 0x89, 0xfd,
-      0x75, 0xd1, 0xda, 0x92, 0xc3, 0x13, 0xc6, 0x76, 0x51, 0x11, 0x40, 0x7b,
-      0x82, 0xf7, 0x30, 0x79, 0x49, 0x04, 0xe3, 0xbb, 0x61, 0x34, 0xa6, 0x58,
-      0x0b, 0x7d, 0xef, 0x3e, 0xf9, 0xb3, 0x8d, 0x2a, 0xba, 0xe9, 0xbc, 0xc0,
-      0xa7, 0xe6, 0x6c, 0xda, 0xf8, 0x8c, 0xdf, 0x8d, 0x96, 0x83, 0x2d, 0x80,
-      0x4f, 0x21, 0x81, 0xde, 0x57, 0x9d, 0x0a, 0x3c, 0xcc, 0xec, 0x3b, 0xb2,
-      0x25, 0x96, 0x3c, 0xea, 0xfd, 0x46, 0x26, 0xbe, 0x1c, 0x79, 0x82, 0x1d,
-      0xe0, 0x14, 0x22, 0x7c, 0x80, 0x3d, 0xbd, 0x05, 0x90, 0xfa, 0xaf, 0x7d,
-      0x70, 0x13, 0x43, 0x0f, 0x3d, 0xa0, 0x7f, 0x92, 0x3a, 0x53, 0x69, 0xe4,
-      0xb0, 0x10, 0x0d, 0xa7, 0x73, 0xa8, 0x8c, 0x74, 0xab, 0xd7, 0x78, 0x15,
-      0x45, 0xec, 0x6e, 0xc8, 0x8b, 0xa0, 0xba, 0x21, 0x6f, 0xf3, 0x08, 0xb8,
-      0xc7, 0x4f, 0x14, 0xf5, 0xcc, 0xfd, 0x39, 0xbc, 0x11, 0xf5, 0xb9, 0x11,
-      0xba, 0xf3, 0x11, 0x24, 0x74, 0x3e, 0x0c, 0x07, 0x4f, 0xac, 0x2a, 0xb2,
-      0xb1, 0x3c, 0x00, 0xfa, 0xbb, 0x8c, 0xd8, 0x7d, 0x17, 0x5b, 0x8d, 0x39,
-      0xc6, 0x23, 0x31, 0x32, 0x7d, 0x6e, 0x20, 0x38, 0xd0, 0xc3, 0x58, 0xe2,
-      0xb1, 0xfe, 0x53, 0x6b, 0xc7, 0x10, 0x13, 0x7e, 0xc6, 0x7c, 0x67, 0x59,
-      0x43, 0x70, 0x4a, 0x2d, 0x7f, 0x76, 0xde, 0xbd, 0x45, 0x43, 0x56, 0x60,
-      0xcd, 0xe9, 0x24, 0x7b, 0xb7, 0x41, 0xce, 0x56, 0xed, 0xd3, 0x74, 0x75,
-      0xcc, 0x9d, 0x48, 0x61, 0xc8, 0x19, 0x66, 0x08, 0xfb, 0x28, 0x60, 0x1f,
-      0x83, 0x11, 0xc0, 0x9b, 0xbd, 0x71, 0x53, 0x36, 0x01, 0x76, 0xa8, 0xc0,
-      0xdc, 0x1d, 0x18, 0x85, 0x19, 0x65, 0xce, 0xcf, 0x14, 0x2e, 0x6c, 0x32,
-      0x15, 0xbc, 0x2c, 0x5e, 0x8f, 0xfc, 0x3c, 0xf0, 0x2d, 0xf5, 0x5c, 0x04,
-      0xc9, 0x22, 0xf4, 0xc3, 0xb8, 0x57, 0x79, 0x52, 0x41, 0xfd, 0xff, 0xcd,
-      0x26, 0xa8, 0xc0, 0xd2, 0xe1, 0x71, 0xd6, 0xf1, 0xf4, 0x0c, 0xa8, 0xeb,
-      0x0c, 0x33, 0x40, 0x25, 0x73, 0xbb, 0x31, 0xda, 0x0c, 0xa6, 0xee, 0x0c,
-      0x41, 0x51, 0x94, 0x3c, 0x24, 0x27, 0x65, 0xe9, 0xb5, 0xc4, 0xe2, 0x88,
-      0xc0, 0x82, 0xd0, 0x72, 0xd9, 0x10, 0x4d, 0x7f, 0xc0, 0x88, 0x94, 0x41,
-      0x2d, 0x05, 0x09, 0xfb, 0x97, 0x31, 0x6e, 0xc1, 0xe9, 0xf4, 0x50, 0x70,
-      0xdc, 0x3f, 0x0a, 0x90, 0x46, 0x37, 0x60, 0x8c, 0xfb, 0x06, 0x6e, 0xde,
-      0x6f, 0xa7, 0x6b, 0xa3, 0x88, 0x18, 0x96, 0x93, 0x19, 0x87, 0xe7, 0x0a,
-      0x98, 0xf0, 0x13, 0x01, 0xab, 0x7c, 0xeb, 0x25, 0xa5, 0xe2, 0x98, 0x44,
-      0x7d, 0x09, 0xe2, 0x42, 0x33, 0xd4, 0xeb, 0xcc, 0x9b, 0x70, 0xf6, 0x0f,
-      0xf0, 0xb2, 0x99, 0xcc, 0x4f, 0x64, 0xc4, 0x69, 0x12, 0xea, 0x56, 0xfe,
-      0x50, 0x0e, 0x02, 0x1f, 0x6d, 0x7a, 0x79, 0x62, 0xaa, 0x2e, 0x52, 0xaf,
-      0xa3, 0xed, 0xcd, 0xa7, 0x45, 0xe6, 0x86, 0xed, 0xa1, 0x73, 0x5b, 0x1e,
-      0x49, 0x4f, 0x92, 0x50, 0x83, 0x99, 0x3c, 0xf4, 0xf6, 0xa8, 0x49, 0xd7,
-      0x08, 0xf7, 0xdc, 0x28, 0x2c, 0xe6, 0x22, 0x6f, 0xf8, 0xfa, 0xba, 0x9e,
-      0x0a, 0xcf, 0x72, 0x74, 0x76, 0x75, 0x99, 0x4d, 0x3d, 0x9a, 0x4c, 0x54,
-      0xcd, 0xf8, 0x54, 0xf0, 0xbd, 0x73, 0xe9, 0x4f, 0x29, 0xd0, 0xe1, 0x24,
-      0x94, 0x52, 0xd6, 0x60, 0x80, 0x71, 0x24, 0x95, 0x92, 0x01, 0x0e, 0xa9,
-      0x7e, 0x64, 0x2e, 0xed, 0x51, 0xcc, 0xd2, 0xff, 0xfd, 0x0b,
+      0xe0, 0xc0, 0x77, 0xeb, 0x7a, 0x48, 0x7d, 0x74, 0x4e, 0x4f, 0x6d, 0xb9,
+      0x5c, 0x18, 0xe9, 0x5b, 0x47, 0x6c, 0x78, 0x9d, 0x98, 0x02, 0x84, 0x9f,
+      0xf2, 0x45, 0x43, 0x86, 0x0e, 0xc6, 0x93, 0x48, 0xd8, 0x20, 0xff, 0x82,
+      0x38, 0x9e, 0x78, 0xb4, 0x2c, 0xb3, 0x42, 0xe4, 0xb3, 0xab, 0xdf, 0xed,
+      0x65, 0x24, 0x0c, 0xa5, 0x95, 0x2c, 0xbf, 0x4c, 0x28, 0xfc, 0xb8, 0xe7,
+      0xc6, 0xbc, 0x76, 0xa0, 0xf5, 0x3f, 0x29, 0x73, 0x23, 0xf1, 0x6c, 0x10,
+      0x7c, 0x08, 0x8e, 0x16, 0x3a, 0xda, 0x17, 0xa3, 0x0d, 0x46, 0x44, 0xee,
+      0x6f, 0x70, 0xf1, 0x88, 0x51, 0x35, 0x33, 0x91, 0x76, 0xeb, 0x98, 0xc1,
+      0x04, 0xdb, 0x97, 0xab, 0x88, 0xb9, 0x04, 0x87, 0xd9, 0xb8, 0x34, 0xd3,
+      0x38, 0xe7, 0x90, 0x05, 0x2e, 0x45, 0xe0, 0xac, 0x36, 0x0c, 0x59, 0x58,
+      0xb1, 0xf5, 0x65, 0x6d, 0x28, 0x1a, 0x39, 0xd9, 0xd2, 0x83, 0x17, 0xee,
+      0xeb, 0x6f, 0x7d, 0x29, 0x3c, 0x79, 0xcf, 0x48, 0xf1, 0x6d, 0x35, 0xc2,
+      0x8c, 0xe8, 0x67, 0x18, 0xcc, 0x9d, 0x9b, 0x8d, 0x07, 0x7a, 0x4e, 0x56,
+      0xa8, 0x00, 0x2e, 0x67, 0x67, 0xbb, 0xc1, 0xda, 0x4a, 0x7b, 0x9f, 0xa6,
+      0x4a, 0x5c, 0x40, 0xcc, 0xe4, 0xdd, 0xf5, 0xc0, 0x44, 0xfe, 0xa5, 0xa2,
+      0x1c, 0xdc, 0xf2, 0x31, 0xf4, 0x01, 0x1f, 0x69, 0x15, 0x7e, 0x8c, 0x54,
+      0xb6, 0x47, 0x0c, 0x1d, 0x9f, 0x1a, 0xfa, 0xf7, 0x46, 0xa3, 0xcb, 0x34,
+      0x2c, 0x18, 0x45, 0x65, 0xc4, 0xf2, 0x0e, 0xf8, 0xc7, 0x96, 0x1d, 0x29,
+      0x5c, 0x90, 0xd3, 0xdf, 0xb2, 0x8e, 0x21, 0xf9, 0x15, 0x40, 0x7e, 0xd3,
+      0x84, 0x52, 0x1d, 0xd9, 0xee, 0xed, 0xe8, 0x71, 0x1c, 0xdb, 0x48, 0xf5,
+      0x20, 0x82, 0xc4, 0x61, 0xfd, 0x6d, 0x71, 0x9f, 0xd8, 0x03, 0x90, 0x8e,
+      0xfc, 0xed, 0x4d, 0xab, 0x6e, 0xb2, 0xe9, 0x66, 0xfd, 0xcc, 0x3a, 0xa3,
+      0x99, 0x53, 0x35, 0x76, 0xea, 0x08, 0x88, 0xba, 0xf0, 0xb7, 0x53, 0xf3,
+      0x4c, 0x1a, 0x8f, 0x7f, 0xe4, 0x1b, 0x8b, 0xfc, 0x99, 0x3e, 0x4c, 0xa9,
+      0xd9, 0x17, 0x10, 0x64, 0x60, 0xfd, 0x81, 0x76, 0xe6, 0x37, 0xb0, 0xe3,
+      0x3e, 0xc0, 0xf7, 0x06, 0x7e, 0x34, 0xa5, 0xf4, 0xb9, 0x5f, 0x66, 0xe6,
+      0x81, 0xc8, 0x5e, 0xb2, 0x26, 0x6b, 0x8c, 0xad, 0xd0, 0x94, 0x01, 0x22,
+      0xf6, 0xbe, 0x1a, 0x0b, 0x34, 0xfc, 0x33, 0xc0, 0x84, 0xa5, 0xe0, 0x12,
+      0x8a, 0x08, 0xae, 0x8a, 0xaf, 0x55, 0x0c, 0x34, 0x4b, 0x2b, 0xdd, 0xa3,
+      0x7c, 0xc0, 0xed, 0xe8, 0x8d, 0x98, 0x47, 0x7c, 0x81, 0x25, 0x1b, 0x9f,
+      0x08, 0x26, 0x9d, 0xfc, 0x19, 0x8e, 0x39, 0xc4, 0x1a, 0x3c, 0x42, 0x70,
+      0x49, 0x37, 0x57, 0x87, 0x0f, 0x76, 0xb1, 0xc4, 0xbe, 0x25, 0x5e, 0x1c,
+      0x06, 0x57, 0xc6, 0x88, 0x34, 0x28, 0xdf, 0x60, 0x33, 0x09, 0xc5, 0xcc,
+      0xf4, 0xc4, 0x33, 0x85, 0x8b, 0x48, 0xe8, 0x27, 0xb7, 0x72, 0x22, 0x44,
+      0xff, 0xe7, 0x89, 0xf9, 0x71, 0x99, 0xed, 0x62, 0x47, 0xb0, 0x22, 0x9e,
+      0xa6, 0x7c, 0xaf, 0xa9, 0x98, 0x2b, 0x5c, 0x8a, 0x42, 0x34, 0x77, 0xa3,
+      0xc8, 0x13, 0x1e, 0xcf, 0x32, 0xa7, 0x70, 0xa8, 0xad, 0xc1, 0x66, 0x5c,
+      0x8f, 0xaf, 0x14, 0x6d, 0xc4, 0x45, 0x05, 0xcd, 0xcb, 0x80, 0xfa, 0x0e,
+      0xa6, 0xca, 0x72, 0x86, 0xd2, 0xb7, 0x39, 0x26, 0x77, 0xf8, 0x14, 0xd0,
+      0xcd, 0xdd, 0xf7, 0xdc, 0xda, 0x25, 0x8e, 0x3c, 0x21, 0xfd, 0xef, 0x92,
+      0xee, 0x52, 0xf7, 0xc3, 0xc7, 0xe2, 0x2d, 0x1c, 0x57, 0x5a, 0xba, 0xd8,
+      0xaa, 0x0d, 0x09, 0xa7, 0xb3, 0xcc, 0xa1, 0x5d, 0xdb, 0x04, 0x21, 0x82,
+      0xef, 0xba, 0xc2, 0xc8, 0x54, 0xb1, 0xbe, 0xd7, 0x2a, 0x91, 0xd8, 0xeb,
+      0x72, 0x54, 0xc1, 0x74, 0x24, 0x24, 0x5a, 0x03, 0xf7, 0xcd, 0xab, 0x91,
+      0xd1, 0x63, 0xf1, 0x60, 0x9f, 0x22, 0x07, 0xad, 0x10, 0x2b, 0x97, 0x1c,
+      0x6f, 0xce, 0xc0, 0x29, 0xc2, 0xb2, 0xb8, 0x1b, 0xbd, 0x14, 0xc8, 0xb9,
+      0x80, 0x66, 0xc1, 0x86, 0xfc, 0x93, 0x5f, 0x6e, 0x0b, 0x7a, 0x7b, 0x8e,
+      0x42, 0x8c, 0x08, 0xd1, 0x60, 0xb9, 0xf8, 0x66, 0x24, 0x7d, 0x88, 0x58,
+      0x2f, 0xd2, 0x52, 0x75, 0x3a, 0x8a, 0x1c, 0xfa, 0x1e, 0xa1, 0x1c, 0x91,
+      0x46, 0x79, 0x9a, 0xe5, 0x8a, 0xdd, 0xc2, 0x75, 0xed, 0x0d, 0xb8, 0x2b,
+      0x4f, 0x8f, 0x95, 0xca, 0xce, 0x21, 0xa4, 0x7a, 0x0d, 0x14, 0x7f, 0x2d,
+      0x98, 0xf0, 0x88, 0xc3, 0x6f, 0xad, 0xb5, 0x04, 0x24, 0x91, 0x41, 0x65,
+      0xd3, 0xa5, 0x7e, 0xfb, 0x53, 0x1c, 0xcc, 0xd0, 0xf7, 0x7c, 0x91, 0x08,
+      0x0e, 0xdd, 0xd4, 0x6c, 0x73, 0xaa, 0xa5, 0x7a, 0xd2, 0x24, 0xc9, 0x3b,
+      0x6f, 0xda, 0x06, 0x8a, 0xdb, 0x2e, 0xa8, 0xe9, 0xe1, 0x3e, 0x08, 0xee,
+      0xbe, 0x96, 0x65, 0x72, 0x68, 0x6f, 0xf7, 0x50, 0xe7, 0xa7, 0x18, 0xda,
+      0xc2, 0x94, 0xda, 0xe3, 0xbc, 0xca, 0x03, 0xd8, 0xf7, 0x7a, 0xcc, 0x44,
+      0xa1, 0x60, 0xa8, 0x7f, 0xdc, 0xef, 0x80, 0xf4, 0x62, 0xc6, 0x06, 0x4e,
+      0xb6, 0xac, 0x77, 0x17, 0xb7, 0xb3, 0x3e, 0xf8, 0x6d, 0x8a, 0x61, 0x83,
+      0x3a, 0xfd, 0xbb, 0x93, 0x5b, 0x1a, 0x33, 0xf8, 0xee, 0x7d, 0x9e, 0x5c,
+      0xf8, 0xc9, 0xd5, 0x3e, 0x3d, 0x42, 0x9b, 0xe5, 0x0d, 0xec, 0xc9, 0x0f,
+      0x6f, 0x03, 0xb0, 0x41, 0x85, 0xb9, 0xfe, 0xf9, 0xb1, 0xb4, 0xc3, 0xd9,
+      0x13, 0x03, 0xfa, 0x0d, 0xe7, 0xd1, 0xb4, 0xc8, 0xf6, 0xb5, 0x11, 0x7a,
+      0x92, 0x09, 0x21, 0x7b, 0xa9, 0x89, 0x4c, 0x19, 0x90, 0x0d, 0x96, 0x32,
+      0x4f, 0x77, 0xfc, 0x7f, 0x8c, 0xa3, 0x39, 0x2a, 0x56, 0xe6, 0x5c, 0xd1,
+      0x86, 0x0a, 0x72, 0xf4, 0xa3, 0x1b, 0xa5, 0x30, 0x04, 0x3c, 0x15, 0x20,
+      0x4b, 0xe4, 0x2d, 0x1a, 0xf1, 0x44, 0x48, 0xfc, 0xda, 0xc1, 0x41, 0xdb,
+      0x71, 0xfd, 0x92, 0x00, 0x53, 0xe4, 0x70, 0xd0, 0xba, 0xf6, 0xef, 0x17,
+      0x72, 0xb8, 0xea, 0x6d, 0x41, 0x16, 0x4d, 0x1f, 0x59, 0x18, 0xbd, 0x1f,
+      0xc5, 0x6b, 0x6a, 0x6c, 0x2e, 0xa6, 0x1a, 0x33, 0x74, 0x8b, 0xc5, 0x9f,
+      0x16, 0x01, 0x77, 0x7e, 0x37, 0xe7, 0x63, 0xe1, 0xa3, 0x8c, 0x1f, 0x71,
+      0xe9, 0x4f, 0xad, 0x15, 0x8b, 0xf3, 0xc9, 0xac, 0xdc, 0x19, 0xad, 0x92,
+      0x18, 0x00, 0xf6, 0xa1, 0xd5, 0x97, 0xa3, 0x3d, 0x9e, 0x78, 0x02, 0xc3,
+      0x8f, 0x75, 0xd8, 0xad, 0x22, 0xbf, 0xef, 0x19, 0x5d, 0x15, 0x34, 0x1a,
+      0x7c, 0x9b, 0xaf, 0xd4, 0xf2, 0xf9, 0x5f, 0x72, 0x88, 0x9c, 0xe4, 0x58,
+      0xda, 0x46, 0x8f, 0x79, 0x30, 0x2b, 0xd9, 0x3b, 0xbc, 0xab, 0x28, 0x77,
+      0x75, 0x0e, 0x2c, 0x23, 0x47, 0x95, 0x14, 0xeb, 0xf0, 0x4a, 0x3e, 0x53,
+      0x93, 0xa7, 0xf4, 0x82, 0x9c, 0x34, 0x8b, 0x80, 0x42, 0xb2, 0xa7, 0xb0,
+      0x7c, 0x6c, 0xe1, 0x07, 0xf4, 0x34, 0x3e, 0xed, 0x33, 0x9c, 0xb3, 0xde,
+      0xa5, 0x91, 0x61, 0x25, 0x8e, 0x8c, 0x54, 0x56, 0xbe, 0x1a, 0xac, 0x17,
+      0xd2, 0x7a, 0xa4, 0x12, 0x54, 0x2a, 0x51, 0xd0, 0x0e, 0xd1, 0xc1, 0x44,
+      0x50, 0x05, 0x39, 0xa7, 0xb6, 0x14, 0x45, 0xca, 0xf8, 0x5f, 0x06, 0x6b,
+      0x5d, 0x5e, 0xc7, 0xe9, 0x27, 0x6f, 0x38, 0xe0, 0x31, 0xcf, 0xf8, 0xcc,
+      0x2e, 0xb9, 0x4a, 0x10, 0x1b, 0xb4, 0x34, 0x4b, 0x90, 0xbb, 0xf2, 0xe0,
+      0x3c, 0x79, 0x7f, 0x39, 0x59, 0x0c, 0x01, 0x4c, 0x0d, 0x2d, 0x71, 0xf1,
+      0xbd, 0xda, 0x1a, 0x78, 0xcf, 0x26, 0x6f, 0xb5, 0xa9, 0x07, 0x20, 0xe6,
+      0x8c, 0xd0, 0xad, 0xd4, 0xca, 0x24, 0x6c, 0xc5, 0x28, 0x1d, 0xfb, 0xcc,
+      0xe7, 0x93, 0x72, 0x99, 0x61, 0x63, 0x60, 0x4c, 0x5c, 0xa9, 0xb6, 0x15,
+      0x32, 0xa4, 0xbc, 0x1f, 0xf6, 0x63, 0x61, 0x2c, 0x26, 0xa7, 0x0e, 0x5f,
+      0x1b, 0x25, 0xce, 0x3f, 0x64, 0xdf, 0x6d, 0xb0, 0x8f, 0xd2, 0xe9, 0x3b,
+      0x35, 0xd0, 0x59, 0x81, 0x22, 0xf1, 0x65, 0x86, 0x15, 0x10, 0xe8, 0xa7,
+      0xa1, 0x6f, 0xb4, 0x34, 0x1c, 0x79, 0xd5, 0x9e, 0x8d, 0xc8, 0xa5, 0xbb,
+      0x82, 0x71, 0x81, 0x00, 0x34, 0x55, 0x6b, 0x96, 0x56, 0x13, 0x0e, 0xe7,
+      0x39, 0xa2, 0x6f, 0xbe, 0x54, 0x2a, 0x13, 0x03, 0x13, 0xd2, 0x1d, 0x71,
+      0x9a, 0xbe, 0x09, 0x00, 0xe1, 0x8d, 0x59, 0xb5, 0x44, 0x02,
   };
   EXPECT_EQ(Bytes(ciphertext), Bytes(kExpectedCiphertext));
 
   static const uint8_t kExpectedSharedKey[HRSS_KEY_BYTES] = {
-      0xbc, 0x98, 0x9c, 0x9c, 0x1f, 0x57, 0x6f, 0x38, 0x0b, 0x5d, 0xc2,
-      0x23, 0x7d, 0x01, 0xae, 0x63, 0x17, 0xe8, 0xe4, 0xb2, 0x02, 0xa7,
-      0xc4, 0x3a, 0x1b, 0x5a, 0xf3, 0xf8, 0xb5, 0xea, 0x6e, 0x22,
+      0x57, 0xf2, 0x77, 0xb2, 0xf3, 0x7f, 0xd0, 0x71, 0xb6, 0x7e, 0x64,
+      0x0f, 0x85, 0x1f, 0x6d, 0x3b, 0xd1, 0x7a, 0x6e, 0x01, 0x04, 0xde,
+      0x0f, 0x9e, 0x03, 0x95, 0x55, 0x60, 0xce, 0xda, 0x32, 0x71,
   };
   EXPECT_EQ(Bytes(shared_key), Bytes(kExpectedSharedKey));
 
@@ -472,9 +473,9 @@
   HRSS_decap(shared_key, &priv, ciphertext, sizeof(ciphertext));
 
   static const uint8_t kExpectedFailureKey[HRSS_KEY_BYTES] = {
-      0x8e, 0x19, 0xfe, 0x2b, 0x12, 0x67, 0xef, 0x9a, 0x63, 0x4d, 0x79,
-      0x33, 0x8c, 0xce, 0xbf, 0x03, 0xdb, 0x9c, 0xc4, 0xc1, 0x70, 0xe1,
-      0x32, 0xa6, 0xb3, 0xd3, 0xa1, 0x43, 0x3c, 0xf1, 0x1f, 0x5a,
+      0x13, 0xf7, 0xed, 0x51, 0x00, 0xbc, 0xca, 0x29, 0xdf, 0xb0, 0xd0,
+      0x5e, 0xa1, 0x9d, 0x15, 0xb2, 0xf6, 0x23, 0x94, 0xfd, 0x93, 0x74,
+      0x14, 0x46, 0x85, 0x61, 0x8b, 0x87, 0x30, 0xd3, 0x8d, 0xad,
   };
   EXPECT_EQ(Bytes(shared_key), Bytes(kExpectedFailureKey));
 }
diff --git a/include/openssl/hrss.h b/include/openssl/hrss.h
index d4e16dc..5390696 100644
--- a/include/openssl/hrss.h
+++ b/include/openssl/hrss.h
@@ -38,9 +38,8 @@
 
 // HRSS_SAMPLE_BYTES is the number of bytes of entropy needed to generate a
 // short vector. There are 701 coefficients, but the final one is always set to
-// zero when sampling. Otherwise, one byte of input is enough to generate two
-// coefficients.
-#define HRSS_SAMPLE_BYTES ((701 - 1) / 2)
+// zero when sampling. Otherwise, we need one byte of input per coefficient.
+#define HRSS_SAMPLE_BYTES (701 - 1)
 // HRSS_GENERATE_KEY_BYTES is the number of bytes of entropy needed to generate
 // an HRSS key pair.
 #define HRSS_GENERATE_KEY_BYTES (HRSS_SAMPLE_BYTES + HRSS_SAMPLE_BYTES + 32)