diff --git a/go.mod b/go.mod
index 78d0feccd1a1..18c41928d458 100644
--- a/go.mod
+++ b/go.mod
@@ -84,6 +84,7 @@ require (
 	github.com/FactomProject/btcutilecc v0.0.0-20130527213604-d3a63a5752ec // indirect
 	github.com/Microsoft/go-winio v0.6.1 // indirect
 	github.com/VictoriaMetrics/fastcache v1.12.1 // indirect
+	github.com/ava-labs/simplex v0.0.0-20250611154800-78b82e9820e5
 	github.com/beorn7/perks v1.0.1 // indirect
 	github.com/bits-and-blooms/bitset v1.10.0 // indirect
 	github.com/btcsuite/btcd/btcec/v2 v2.3.2 // indirect
diff --git a/go.sum b/go.sum
index e2231bc73fbc..5eedbfcb4301 100644
--- a/go.sum
+++ b/go.sum
@@ -72,6 +72,8 @@ github.com/ava-labs/ledger-avalanche/go v0.0.0-20241009183145-e6f90a8a1a60 h1:EL
 github.com/ava-labs/ledger-avalanche/go v0.0.0-20241009183145-e6f90a8a1a60/go.mod h1:/7qKobTfbzBu7eSTVaXMTr56yTYk4j2Px6/8G+idxHo=
 github.com/ava-labs/libevm v0.0.0-20250610142802-2672fbd7cdfc h1:cSXaUY4hdmoJ2FJOgOzn+WiovN/ZB/zkNRgnZhE50OA=
 github.com/ava-labs/libevm v0.0.0-20250610142802-2672fbd7cdfc/go.mod h1:+Iol+sVQ1KyoBsHf3veyrBmHCXr3xXRWq6ZXkgVfNLU=
+github.com/ava-labs/simplex v0.0.0-20250611154800-78b82e9820e5 h1:rwPm63i5nJ2XIuNjO2H68gDmMKje0VW7orLZMISPrC8=
+github.com/ava-labs/simplex v0.0.0-20250611154800-78b82e9820e5/go.mod h1:GVzumIo3zR23/qGRN2AdnVkIPHcKMq/D89EGWZfMGQ0=
 github.com/aymerick/raymond v2.0.3-0.20180322193309-b565731e1464+incompatible/go.mod h1:osfaiScAUVup+UC9Nfq76eWqDhXlp+4UYaA8uhTBO6g=
 github.com/beorn7/perks v1.0.1 h1:VlbKKnNfV8bJzeqoa4cOKqO6bYr3WgKZxO8Z16+hsOM=
 github.com/beorn7/perks v1.0.1/go.mod h1:G2ZrVWU2WbWT9wwq4/hrbKbnv/1ERSJQ0ibhJ6rlkpw=
diff --git a/simplex/bls.go b/simplex/bls.go
new file mode 100644
index 000000000000..7530ea55bf4e
--- /dev/null
+++ b/simplex/bls.go
@@ -0,0 +1,124 @@
+// Copyright (C) 2019-2024, Ava Labs, Inc. All rights reserved.
+// See the file LICENSE for licensing terms.
+
+package simplex
+
+import (
+	"errors"
+	"fmt"
+
+	"github.com/ava-labs/simplex"
+
+	"github.com/ava-labs/avalanchego/ids"
+	"github.com/ava-labs/avalanchego/utils/crypto/bls"
+)
+
+var (
+	errSignatureVerificationFailed = errors.New("signature verification failed")
+	errSignerNotFound              = errors.New("signer not found in the membership set")
+	errInvalidNodeID               = errors.New("unable to parse node ID")
+	errFailedToParseSignature      = errors.New("failed to parse signature")
+)
+
+var _ simplex.Signer = (*BLSSigner)(nil)
+
+type SignFunc func(msg []byte) (*bls.Signature, error)
+
+// BLSSigner signs messages encoded with the provided ChainID and NetworkID.
+// using the SignBLS function.
+type BLSSigner struct {
+	chainID   ids.ID
+	networkID uint32
+	// signBLS is passed in because we support both software and hardware BLS signing.
+	signBLS SignFunc
+}
+
+type BLSVerifier struct {
+	nodeID2PK map[ids.NodeID]*bls.PublicKey
+	networkID uint32
+	chainID   ids.ID
+}
+
+func NewBLSAuth(config *Config) (BLSSigner, BLSVerifier) {
+	verifier := createVerifier(config)
+
+	return BLSSigner{
+		chainID:   config.Ctx.ChainID,
+		networkID: config.Ctx.NetworkID,
+		signBLS:   config.SignBLS,
+	}, verifier
+}
+
+// Sign returns a signature on the given message using BLS signature scheme.
+// It encodes the message to sign with the chain ID, and network ID,
+func (s *BLSSigner) Sign(message []byte) ([]byte, error) {
+	message2Sign, err := encodeMessageToSign(message, s.chainID, s.networkID)
+	if err != nil {
+		return nil, fmt.Errorf("failed to encode message to sign: %w", err)
+	}
+
+	sig, err := s.signBLS(message2Sign)
+	if err != nil {
+		return nil, err
+	}
+
+	sigBytes := bls.SignatureToBytes(sig)
+	return sigBytes, nil
+}
+
+type encodedSimplexSignedPayload struct {
+	NewtorkID uint32 `serialize:"true"`
+	ChainID   ids.ID `serialize:"true"`
+	Message   []byte `serialize:"true"`
+}
+
+func encodeMessageToSign(message []byte, chainID ids.ID, networkID uint32) ([]byte, error) {
+	encodedSimplexMessage := encodedSimplexSignedPayload{
+		Message:   message,
+		ChainID:   chainID,
+		NewtorkID: networkID,
+	}
+	return Codec.Marshal(CodecVersion, &encodedSimplexMessage)
+}
+
+func (v BLSVerifier) Verify(message []byte, signature []byte, signer simplex.NodeID) error {
+	key, err := ids.ToNodeID(signer)
+	if err != nil {
+		return fmt.Errorf("%w: %w", errInvalidNodeID, err)
+	}
+
+	pk, exists := v.nodeID2PK[key]
+	if !exists {
+		return fmt.Errorf("%w: signer %x", errSignerNotFound, key)
+	}
+
+	sig, err := bls.SignatureFromBytes(signature)
+	if err != nil {
+		return fmt.Errorf("%w: %w", errFailedToParseSignature, err)
+	}
+
+	message2Verify, err := encodeMessageToSign(message, v.chainID, v.networkID)
+	if err != nil {
+		return fmt.Errorf("failed to encode message to verify: %w", err)
+	}
+
+	if !bls.Verify(pk, sig, message2Verify) {
+		return errSignatureVerificationFailed
+	}
+
+	return nil
+}
+
+func createVerifier(config *Config) BLSVerifier {
+	verifier := BLSVerifier{
+		nodeID2PK: make(map[ids.NodeID]*bls.PublicKey),
+		networkID: config.Ctx.NetworkID,
+		chainID:   config.Ctx.ChainID,
+	}
+
+	for _, node := range config.Validators {
+		verifier.nodeID2PK[node.NodeID] = node.PublicKey
+	}
+
+	return verifier
+}
diff --git a/simplex/bls_test.go b/simplex/bls_test.go
new file mode 100644
index 000000000000..cc38dd6d918d
--- /dev/null
+++ b/simplex/bls_test.go
@@ -0,0 +1,88 @@
+// Copyright (C) 2019-2024, Ava Labs, Inc. All rights reserved.
+// See the file LICENSE for licensing terms.
+
+package simplex
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/ava-labs/avalanchego/ids"
+	"github.com/ava-labs/avalanchego/utils/crypto/bls"
+)
+
+func TestBLSVerifier(t *testing.T) {
+	config, err := newEngineConfig()
+	require.NoError(t, err)
+	signer, verifier := NewBLSAuth(config)
+	otherNodeID := ids.GenerateTestNodeID()
+
+	msg := []byte("Begin at the beginning, and go on till you come to the end: then stop")
+	tests := []struct {
+		name      string
+		expectErr error
+		nodeID    []byte
+		sig       []byte
+	}{
+		{
+			name:      "valid_signature",
+			expectErr: nil,
+			nodeID:    config.Ctx.NodeID[:],
+			sig: func() []byte {
+				sig, err := signer.Sign(msg)
+				require.NoError(t, err)
+				return sig
+			}(),
+		},
+		{
+			name:      "not_in_membership_set",
+			expectErr: errSignerNotFound,
+			nodeID:    otherNodeID[:],
+			sig: func() []byte {
+				sig, err := signer.Sign(msg)
+				require.NoError(t, err)
+				return sig
+			}(),
+		},
+		{
+			name:      "invalid_message_encoding",
+			expectErr: errSignatureVerificationFailed,
+			nodeID:    config.Ctx.NodeID[:],
+			sig: func() []byte {
+				sig, err := config.SignBLS(msg)
+				require.NoError(t, err)
+				return bls.SignatureToBytes(sig)
+			}(),
+		},
+		{
+			name:      "invalid_nodeID",
+			expectErr: errInvalidNodeID,
+			nodeID:    []byte{0x01, 0x02, 0x03, 0x04, 0x05}, // Incorrect length NodeID
+			sig: func() []byte {
+				sig, err := signer.Sign(msg)
+				require.NoError(t, err)
+				return sig
+			}(),
+		},
+		{
+			name:      "nil_signature",
+			expectErr: errFailedToParseSignature,
+			nodeID:    config.Ctx.NodeID[:],
+			sig:       nil,
+		},
+		{
+			name:      "malformed_signature",
+			expectErr: errFailedToParseSignature,
+			nodeID:    config.Ctx.NodeID[:],
+			sig:       []byte{0x01, 0x02, 0x03}, // Malformed signature
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err = verifier.Verify(msg, tt.sig, tt.nodeID)
+			require.ErrorIs(t, err, tt.expectErr)
+		})
+	}
+}
diff --git a/simplex/codec.go b/simplex/codec.go
new file mode 100644
index 000000000000..a79200ee4474
--- /dev/null
+++ b/simplex/codec.go
@@ -0,0 +1,26 @@
+// Copyright (C) 2019-2024, Ava Labs, Inc. All rights reserved.
+// See the file LICENSE for licensing terms.
+
+package simplex
+
+import (
+	"math"
+
+	"github.com/ava-labs/avalanchego/codec"
+	"github.com/ava-labs/avalanchego/codec/linearcodec"
+	"github.com/ava-labs/avalanchego/vms/platformvm/warp"
+)
+
+const CodecVersion = warp.CodecVersion + 1
+
+var Codec codec.Manager
+
+func init() {
+	lc := linearcodec.NewDefault()
+
+	Codec = codec.NewManager(math.MaxInt)
+
+	if err := Codec.RegisterCodec(CodecVersion, lc); err != nil {
+		panic(err)
+	}
+}
diff --git a/simplex/config.go b/simplex/config.go
new file mode 100644
index 000000000000..e95f080e2249
--- /dev/null
+++ b/simplex/config.go
@@ -0,0 +1,36 @@
+// Copyright (C) 2019-2024, Ava Labs, Inc. All rights reserved.
+// See the file LICENSE for licensing terms.
+
+package simplex
+
+import (
+	"github.com/ava-labs/avalanchego/ids"
+	"github.com/ava-labs/avalanchego/snow/validators"
+	"github.com/ava-labs/avalanchego/utils/logging"
+)
+
+// Config wraps all the parameters needed for a simplex engine
+type Config struct {
+	Ctx SimplexChainContext
+	Log logging.Logger
+
+	// Validators is a map of node IDs to their validator information.
+	// This tells the node about the current membership set, and should be consistent
+	// across all nodes in the subnet.
+	Validators map[ids.NodeID]*validators.GetValidatorOutput
+
+	// SignBLS is the signing function used for this node to sign messages.
+	SignBLS SignFunc
+}
+
+// Context is information about the current execution.
+type SimplexChainContext struct {
+	// Network is the ID of the network this context exists within.
+	NodeID ids.NodeID
+
+	// ChainID is the ID of the chain this context exists within.
+	ChainID ids.ID
+
+	// NodeID is the ID of this node
+	NetworkID uint32
+}
diff --git a/simplex/test_util.go b/simplex/test_util.go
new file mode 100644
index 000000000000..5b167bd17e8d
--- /dev/null
+++ b/simplex/test_util.go
@@ -0,0 +1,46 @@
+// Copyright (C) 2019-2024, Ava Labs, Inc. All rights reserved.
+// See the file LICENSE for licensing terms.
+
+package simplex
+
+import (
+	"github.com/ava-labs/avalanchego/ids"
+	"github.com/ava-labs/avalanchego/snow/validators"
+	"github.com/ava-labs/avalanchego/utils/constants"
+	"github.com/ava-labs/avalanchego/utils/crypto/bls/signer/localsigner"
+)
+
+func newTestValidatorInfo(allVds []validators.GetValidatorOutput) map[ids.NodeID]*validators.GetValidatorOutput {
+	vds := make(map[ids.NodeID]*validators.GetValidatorOutput, len(allVds))
+	for _, vd := range allVds {
+		vds[vd.NodeID] = &vd
+	}
+
+	return vds
+}
+
+func newEngineConfig() (*Config, error) {
+	ls, err := localsigner.New()
+	if err != nil {
+		return nil, err
+	}
+
+	nodeID := ids.GenerateTestNodeID()
+
+	simplexChainContext := SimplexChainContext{
+		NodeID:    nodeID,
+		ChainID:   ids.GenerateTestID(),
+		NetworkID: constants.UnitTestID,
+	}
+
+	nodeInfo := validators.GetValidatorOutput{
+		NodeID:    nodeID,
+		PublicKey: ls.PublicKey(),
+	}
+
+	return &Config{
+		Ctx:        simplexChainContext,
+		Validators: newTestValidatorInfo([]validators.GetValidatorOutput{nodeInfo}),
+		SignBLS:    ls.Sign,
+	}, nil
+}