Resolve undefined behavior in Ed25519 code

Use multiplications instead of shifting directly.

1 files changed, 73 insertions, 69 deletions

diff --git a/src/lib/pubkey/ed25519/sc_reduce.cpp b/src/lib/pubkey/ed25519/sc_reduce.cpp
index 93dcc6de8..5765c7dac 100644
--- a/src/lib/pubkey/ed25519/sc_reduce.cpp
+++ b/src/lib/pubkey/ed25519/sc_reduce.cpp
@@ -24,6 +24,10 @@ Output:
 
 void sc_reduce(uint8_t* s)
    {
+   const int64_t X20 = (1 << 20);
+   const int64_t X21 = (1 << 21);
+
+
    int64_t s0 = 2097151 & load_3(s);
    int64_t s1 = 2097151 & (load_4(s + 2) >> 5);
    int64_t s2 = 2097151 & (load_3(s + 5) >> 2);
@@ -114,40 +118,40 @@ void sc_reduce(uint8_t* s)
    s11 -= s18 * 683901;
    s18 = 0;
 
-   carry6 = (s6 + (1<<20)) >> 21;
+   carry6 = (s6 + X20) >> 21;
    s7 += carry6;
-   s6 -= carry6 << 21;
-   carry8 = (s8 + (1<<20)) >> 21;
+   s6 -= carry6 * X21;
+   carry8 = (s8 + X20) >> 21;
    s9 += carry8;
-   s8 -= carry8 << 21;
-   carry10 = (s10 + (1<<20)) >> 21;
+   s8 -= carry8 * X21;
+   carry10 = (s10 + X20) >> 21;
    s11 += carry10;
-   s10 -= carry10 << 21;
-   carry12 = (s12 + (1<<20)) >> 21;
+   s10 -= carry10 * X21;
+   carry12 = (s12 + X20) >> 21;
    s13 += carry12;
-   s12 -= carry12 << 21;
-   carry14 = (s14 + (1<<20)) >> 21;
+   s12 -= carry12 * X21;
+   carry14 = (s14 + X20) >> 21;
    s15 += carry14;
-   s14 -= carry14 << 21;
-   carry16 = (s16 + (1<<20)) >> 21;
+   s14 -= carry14 * X21;
+   carry16 = (s16 + X20) >> 21;
    s17 += carry16;
-   s16 -= carry16 << 21;
+   s16 -= carry16 * X21;
 
-   carry7 = (s7 + (1<<20)) >> 21;
+   carry7 = (s7 + X20) >> 21;
    s8 += carry7;
-   s7 -= carry7 << 21;
-   carry9 = (s9 + (1<<20)) >> 21;
+   s7 -= carry7 * X21;
+   carry9 = (s9 + X20) >> 21;
    s10 += carry9;
-   s9 -= carry9 << 21;
-   carry11 = (s11 + (1<<20)) >> 21;
+   s9 -= carry9 * X21;
+   carry11 = (s11 + X20) >> 21;
    s12 += carry11;
-   s11 -= carry11 << 21;
-   carry13 = (s13 + (1<<20)) >> 21;
+   s11 -= carry11 * X21;
+   carry13 = (s13 + X20) >> 21;
    s14 += carry13;
-   s13 -= carry13 << 21;
-   carry15 = (s15 + (1<<20)) >> 21;
+   s13 -= carry13 * X21;
+   carry15 = (s15 + X20) >> 21;
    s16 += carry15;
-   s15 -= carry15 << 21;
+   s15 -= carry15 * X21;
 
    s5 += s17 * 666643;
    s6 += s17 * 470296;
@@ -197,43 +201,43 @@ void sc_reduce(uint8_t* s)
    s5 -= s12 * 683901;
    s12 = 0;
 
-   carry0 = (s0 + (1<<20)) >> 21;
+   carry0 = (s0 + X20) >> 21;
    s1 += carry0;
-   s0 -= carry0 << 21;
-   carry2 = (s2 + (1<<20)) >> 21;
+   s0 -= carry0 * X21;
+   carry2 = (s2 + X20) >> 21;
    s3 += carry2;
-   s2 -= carry2 << 21;
-   carry4 = (s4 + (1<<20)) >> 21;
+   s2 -= carry2 * X21;
+   carry4 = (s4 + X20) >> 21;
    s5 += carry4;
-   s4 -= carry4 << 21;
-   carry6 = (s6 + (1<<20)) >> 21;
+   s4 -= carry4 * X21;
+   carry6 = (s6 + X20) >> 21;
    s7 += carry6;
-   s6 -= carry6 << 21;
-   carry8 = (s8 + (1<<20)) >> 21;
+   s6 -= carry6 * X21;
+   carry8 = (s8 + X20) >> 21;
    s9 += carry8;
-   s8 -= carry8 << 21;
-   carry10 = (s10 + (1<<20)) >> 21;
+   s8 -= carry8 * X21;
+   carry10 = (s10 + X20) >> 21;
    s11 += carry10;
-   s10 -= carry10 << 21;
+   s10 -= carry10 * X21;
 
-   carry1 = (s1 + (1<<20)) >> 21;
+   carry1 = (s1 + X20) >> 21;
    s2 += carry1;
-   s1 -= carry1 << 21;
-   carry3 = (s3 + (1<<20)) >> 21;
+   s1 -= carry1 * X21;
+   carry3 = (s3 + X20) >> 21;
    s4 += carry3;
-   s3 -= carry3 << 21;
-   carry5 = (s5 + (1<<20)) >> 21;
+   s3 -= carry3 * X21;
+   carry5 = (s5 + X20) >> 21;
    s6 += carry5;
-   s5 -= carry5 << 21;
-   carry7 = (s7 + (1<<20)) >> 21;
+   s5 -= carry5 * X21;
+   carry7 = (s7 + X20) >> 21;
    s8 += carry7;
-   s7 -= carry7 << 21;
-   carry9 = (s9 + (1<<20)) >> 21;
+   s7 -= carry7 * X21;
+   carry9 = (s9 + X20) >> 21;
    s10 += carry9;
-   s9 -= carry9 << 21;
-   carry11 = (s11 + (1<<20)) >> 21;
+   s9 -= carry9 * X21;
+   carry11 = (s11 + X20) >> 21;
    s12 += carry11;
-   s11 -= carry11 << 21;
+   s11 -= carry11 * X21;
 
    s0 += s12 * 666643;
    s1 += s12 * 470296;
@@ -245,40 +249,40 @@ void sc_reduce(uint8_t* s)
 
    carry0 = s0 >> 21;
    s1 += carry0;
-   s0 -= carry0 << 21;
+   s0 -= carry0 * X21;
    carry1 = s1 >> 21;
    s2 += carry1;
-   s1 -= carry1 << 21;
+   s1 -= carry1 * X21;
    carry2 = s2 >> 21;
    s3 += carry2;
-   s2 -= carry2 << 21;
+   s2 -= carry2 * X21;
    carry3 = s3 >> 21;
    s4 += carry3;
-   s3 -= carry3 << 21;
+   s3 -= carry3 * X21;
    carry4 = s4 >> 21;
    s5 += carry4;
-   s4 -= carry4 << 21;
+   s4 -= carry4 * X21;
    carry5 = s5 >> 21;
    s6 += carry5;
-   s5 -= carry5 << 21;
+   s5 -= carry5 * X21;
    carry6 = s6 >> 21;
    s7 += carry6;
-   s6 -= carry6 << 21;
+   s6 -= carry6 * X21;
    carry7 = s7 >> 21;
    s8 += carry7;
-   s7 -= carry7 << 21;
+   s7 -= carry7 * X21;
    carry8 = s8 >> 21;
    s9 += carry8;
-   s8 -= carry8 << 21;
+   s8 -= carry8 * X21;
    carry9 = s9 >> 21;
    s10 += carry9;
-   s9 -= carry9 << 21;
+   s9 -= carry9 * X21;
    carry10 = s10 >> 21;
    s11 += carry10;
-   s10 -= carry10 << 21;
+   s10 -= carry10 * X21;
    carry11 = s11 >> 21;
    s12 += carry11;
-   s11 -= carry11 << 21;
+   s11 -= carry11 * X21;
 
    s0 += s12 * 666643;
    s1 += s12 * 470296;
@@ -290,37 +294,37 @@ void sc_reduce(uint8_t* s)
 
    carry0 = s0 >> 21;
    s1 += carry0;
-   s0 -= carry0 << 21;
+   s0 -= carry0 * X21;
    carry1 = s1 >> 21;
    s2 += carry1;
-   s1 -= carry1 << 21;
+   s1 -= carry1 * X21;
    carry2 = s2 >> 21;
    s3 += carry2;
-   s2 -= carry2 << 21;
+   s2 -= carry2 * X21;
    carry3 = s3 >> 21;
    s4 += carry3;
-   s3 -= carry3 << 21;
+   s3 -= carry3 * X21;
    carry4 = s4 >> 21;
    s5 += carry4;
-   s4 -= carry4 << 21;
+   s4 -= carry4 * X21;
    carry5 = s5 >> 21;
    s6 += carry5;
-   s5 -= carry5 << 21;
+   s5 -= carry5 * X21;
    carry6 = s6 >> 21;
    s7 += carry6;
-   s6 -= carry6 << 21;
+   s6 -= carry6 * X21;
    carry7 = s7 >> 21;
    s8 += carry7;
-   s7 -= carry7 << 21;
+   s7 -= carry7 * X21;
    carry8 = s8 >> 21;
    s9 += carry8;
-   s8 -= carry8 << 21;
+   s8 -= carry8 * X21;
    carry9 = s9 >> 21;
    s10 += carry9;
-   s9 -= carry9 << 21;
+   s9 -= carry9 * X21;
    carry10 = s10 >> 21;
    s11 += carry10;
-   s10 -= carry10 << 21;
+   s10 -= carry10 * X21;
 
    s[0] = s0 >> 0;
    s[1] = s0 >> 8;