fix: Check bounds before precomputing SRS table (#1846)

* Check bounds before precomputing SRS table

* modify error message

* Fix lint errors

Author: dmanc

encoding/kzg/prover/precompute.go

@@ -100,6 +100,16 @@ func (p *SRSTable) GetSubTables(
 	table, ok := p.Tables[param]
 	if !ok {
 		log.Printf("Table with params: DimE=%v CosetSize=%v does not exist\n", dimE, cosetSize)
+
+		// Check if we have enough SRS points loaded for precomputation
+		// We need polynomial degree m < len(SRS)
+		// (Actually we only access up to index m-cosetSize, but this simpler check is safer)
+		if m >= uint64(len(p.s1)) {
+			return nil, fmt.Errorf("cannot precompute table: insufficient SRS points loaded (have %d, need at least %d). "+
+				"Consider increasing loaded SRS points or using precomputed tables",
+				len(p.s1), m+1)
+		}
+
 		log.Printf("Generating the table. May take a while\n")
 		log.Printf("... ...\n")
 		filename := fmt.Sprintf("dimE%v.coset%v", dimE, cosetSize)

encoding/kzg/prover/precompute_test.go

@@ -9,6 +9,7 @@ import (
 	"github.com/Layr-Labs/eigenda/encoding"
 	"github.com/Layr-Labs/eigenda/encoding/kzg"
 	"github.com/Layr-Labs/eigenda/encoding/kzg/prover"
+	"github.com/consensys/gnark-crypto/ecc/bn254"
 )
 
 func TestNewSRSTable_PreComputeWorks(t *testing.T) {
@@ -43,3 +44,41 @@ func TestNewSRSTable_PreComputeWorks(t *testing.T) {
 	// Result of non precomputed GetSubTables should equal precomputed GetSubTables
 	assert.Equal(t, fftPoints1, fftPoints2)
 }
+
+// This test reproduces the scenario where SRS_LOAD=2097152 and computing a subtable
+// with the parameters (DimE=4, CosetSize=2097152) would cause a panic.
+// The issue: m = numChunks*chunkLen - 1 = 4*2097152 - 1 = 8388607
+// When j=0, k starts at m - cosetSize = 8388607 - 2097152 = 6291455
+// Since 6291455 >= 2097152 (the length of our SRS), we get:
+// panic: runtime error: index out of range [6291455] with length 2097152
+func TestSRSTable_InsufficientSRSPoints_NoPanic(t *testing.T) {
+	// Create a limited SRS with only 2097152 points
+	limitedSRSSize := uint64(2097152)
+	limitedSRS := make([]bn254.G1Affine, limitedSRSSize)
+
+	// Initialize with some dummy points (doesn't matter what they are for this test)
+	var generator bn254.G1Affine
+	_, err := generator.X.SetString("1")
+	require.NoError(t, err)
+	_, err = generator.Y.SetString("2")
+	require.NoError(t, err)
+	for i := range limitedSRS {
+		limitedSRS[i] = generator
+	}
+
+	// Create SRSTable with limited SRS points
+	tempDir := t.TempDir()
+	srsTable, err := prover.NewSRSTable(tempDir, limitedSRS, 1)
+	require.NoError(t, err)
+
+	// Try to create subtables with the following parameters
+	numChunks := uint64(4)
+	chunkLen := uint64(2097152)
+
+	// This should return an error instead of panicking
+	fftPoints, err := srsTable.GetSubTables(numChunks, chunkLen)
+
+	assert.Error(t, err)
+	assert.Nil(t, fftPoints)
+	assert.Contains(t, err.Error(), "insufficient SRS points")
+}