assertion failure in generic-array about elliptic-curves HOT 1 CLOSED

The failing stack frames show:

   4: generic_array::GenericArray<T,N>::from_slice
             at /Users/gus/.cargo/registry/src/github.com-1ecc6299db9ec823/generic-array-0.14.4/src/lib.rs:541:9
   5: k256_test::tests::k256
             at ./src/main.rs:50:19

The lines of code in question are:

            let (r, s): (FieldBytes, FieldBytes) =
                (*FieldBytes::from_slice(r), *FieldBytes::from_slice(s));

This suggests that either r or s are smaller than 64-bytes. The GenericArray::from_slice method will panic if the input is not exactly 64-bytes (in this particular instance, anyway).

r and s are both elements of the scalar field, serialized as big endian integers. As such, if they are smaller than 64-bytes, you'll need to zero-pad them to 64-bytes. Something like:

fn pad_field_element(slice: &[u8; 64]) -> FieldBytes {
    assert!(slice.len() < 64); // or perhaps make the return type `Option<FieldBytes>` and return `None`

    let mut fe_bytes = FieldBytes::default();
    fe_bytes[(64 - slice.len())..].copy_from_slice(slice);
    fe_bytes
}

from elliptic-curves.