getsops/sops · error

failed to generate polynomial: %w

Error message

failed to generate polynomial: %w

What it means

For each byte of the secret, Split() creates a random polynomial via makePolynomial; this error wraps a failure from that helper (typically a randomness-source failure such as rand.Read erroring). The library throws it because without a polynomial it cannot produce shares.

Source

Thrown at shamir/shamir.go:234

	for idx := range out {
		// Store the x coordinate for each part as its last byte
		// Add 1 to the xCoordinate because if the x coordinate is 0,
		// then the result of evaluating the polynomial at that point
		// will be our secret
		out[idx] = make([]byte, len(secret)+1)
		out[idx][len(secret)] = uint8(idx) + 1
	}

	// Construct a random polynomial for each byte of the secret.
	// Because we are using a field of size 256, we can only represent
	// a single byte as the intercept of the polynomial, so we must
	// use a new polynomial for each byte.
	for idx, val := range secret {
		// Create a random polynomial for each point.
		// This polynomial crosses the y axis at `val`.
		p, err := makePolynomial(val, uint8(threshold-1))
		if err != nil {
			return nil, fmt.Errorf("failed to generate polynomial: %w", err)
		}

		// Generate a `parts` number of (x,y) pairs
		// We cheat by encoding the x value once as the final index,
		// so that it only needs to be stored once.
		for i := 0; i < parts; i++ {
			// Add 1 to the xCoordinate because if it's 0,
			// then the result of p.evaluate(x) will be our secret
			x := uint8(i) + 1
			// Evaluate the polynomial at x
			y := p.evaluate(x)
			out[i][idx] = y
		}
	}

	// Return the encoded secrets
	return out, nil
}

View on GitHub (pinned to 13442bb981)

Solutions

1. Fix the underlying entropy source: ensure /dev/urandom is accessible or getrandom(2) works in the runtime environment.
2. Inspect the wrapped %w cause to confirm the rand failure.
3. Retry after environment repair; randomness failures are usually environmental.
4. Check seccomp/AppArmor policies blocking getrandom in containers.

Example fix

// after seeing: failed to generate polynomial: ... /dev/urandom ...
// in Docker, keep default devices and avoid seccomp rules blocking getrandom:
docker run --device /dev/urandom ...

shares, err := shamir.Split(secret, parts, threshold)
if err != nil && strings.Contains(err.Error(), "failed to generate polynomial") {
    // entropy source issue; brief backoff then retry
    time.Sleep(100 * time.Millisecond)
    shares, err = shamir.Split(secret, parts, threshold)
}

When it happens

Trigger: Calling Split with valid args but makePolynomial failing because the system CSPRNG (crypto/rand) fails — e.g. exhausted entropy, broken /dev/urandom in a container.

Common situations: Running in stripped-down containers/chroots where /dev/urandom is unavailable, sandboxed CI environments with restricted syscalls (getrandom blocked).

Related errors

• parts cannot be less than threshold
• parts cannot exceed 255
• threshold must be at least 2
• threshold cannot exceed 255
• cannot split an empty secret

AI-assisted analysis of getsops/sops@13442bb981 (2026-09-01). Data as JSON: /api/errors/ede9938286e90ba0. Report an issue: GitHub.