diff --git a/api/api_full.go b/api/api_full.go
index 057dca8cb..f1dc51efc 100644
--- a/api/api_full.go
+++ b/api/api_full.go
@@ -23,9 +23,9 @@ type FullNode interface {
 	// First message is guaranteed to be of len == 1, and type == 'current'
 	ChainNotify(context.Context) (<-chan []*store.HeadChange, error)
 	ChainHead(context.Context) (*types.TipSet, error)
-	ChainGetRandomness(context.Context, *types.TipSet, []*types.Ticket, int) ([]byte, error)
+	ChainGetRandomness(context.Context, types.TipSetKey, []*types.Ticket, int) ([]byte, error)
 	ChainGetBlock(context.Context, cid.Cid) (*types.BlockHeader, error)
-	ChainGetTipSet(context.Context, []cid.Cid) (*types.TipSet, error)
+	ChainGetTipSet(context.Context, types.TipSetKey) (*types.TipSet, error)
 	ChainGetBlockMessages(context.Context, cid.Cid) (*BlockMessages, error)
 	ChainGetParentReceipts(context.Context, cid.Cid) ([]*types.MessageReceipt, error)
 	ChainGetParentMessages(context.Context, cid.Cid) ([]Message, error)
diff --git a/api/struct.go b/api/struct.go
index 8d14af1d2..d94cc031f 100644
--- a/api/struct.go
+++ b/api/struct.go
@@ -37,19 +37,19 @@ type FullNodeStruct struct {
 	CommonStruct
 
 	Internal struct {
-		ChainNotify            func(context.Context) (<-chan []*store.HeadChange, error)                  `perm:"read"`
-		ChainHead              func(context.Context) (*types.TipSet, error)                               `perm:"read"`
-		ChainGetRandomness     func(context.Context, *types.TipSet, []*types.Ticket, int) ([]byte, error) `perm:"read"`
-		ChainGetBlock          func(context.Context, cid.Cid) (*types.BlockHeader, error)                 `perm:"read"`
-		ChainGetTipSet         func(context.Context, []cid.Cid) (*types.TipSet, error)                    `perm:"read"`
-		ChainGetBlockMessages  func(context.Context, cid.Cid) (*BlockMessages, error)                     `perm:"read"`
-		ChainGetParentReceipts func(context.Context, cid.Cid) ([]*types.MessageReceipt, error)            `perm:"read"`
-		ChainGetParentMessages func(context.Context, cid.Cid) ([]Message, error)                          `perm:"read"`
-		ChainGetTipSetByHeight func(context.Context, uint64, *types.TipSet) (*types.TipSet, error)        `perm:"read"`
-		ChainReadObj           func(context.Context, cid.Cid) ([]byte, error)                             `perm:"read"`
-		ChainSetHead           func(context.Context, *types.TipSet) error                                 `perm:"admin"`
-		ChainGetGenesis        func(context.Context) (*types.TipSet, error)                               `perm:"read"`
-		ChainTipSetWeight      func(context.Context, *types.TipSet) (types.BigInt, error)                 `perm:"read"`
+		ChainNotify            func(context.Context) (<-chan []*store.HeadChange, error)                    `perm:"read"`
+		ChainHead              func(context.Context) (*types.TipSet, error)                                 `perm:"read"`
+		ChainGetRandomness     func(context.Context, types.TipSetKey, []*types.Ticket, int) ([]byte, error) `perm:"read"`
+		ChainGetBlock          func(context.Context, cid.Cid) (*types.BlockHeader, error)                   `perm:"read"`
+		ChainGetTipSet         func(context.Context, types.TipSetKey) (*types.TipSet, error)                `perm:"read"`
+		ChainGetBlockMessages  func(context.Context, cid.Cid) (*BlockMessages, error)                       `perm:"read"`
+		ChainGetParentReceipts func(context.Context, cid.Cid) ([]*types.MessageReceipt, error)              `perm:"read"`
+		ChainGetParentMessages func(context.Context, cid.Cid) ([]Message, error)                            `perm:"read"`
+		ChainGetTipSetByHeight func(context.Context, uint64, *types.TipSet) (*types.TipSet, error)          `perm:"read"`
+		ChainReadObj           func(context.Context, cid.Cid) ([]byte, error)                               `perm:"read"`
+		ChainSetHead           func(context.Context, *types.TipSet) error                                   `perm:"admin"`
+		ChainGetGenesis        func(context.Context) (*types.TipSet, error)                                 `perm:"read"`
+		ChainTipSetWeight      func(context.Context, *types.TipSet) (types.BigInt, error)                   `perm:"read"`
 
 		SyncState       func(context.Context) (*SyncState, error)            `perm:"read"`
 		SyncSubmitBlock func(ctx context.Context, blk *types.BlockMsg) error `perm:"write"`
@@ -245,7 +245,7 @@ func (c *FullNodeStruct) ChainHead(ctx context.Context) (*types.TipSet, error) {
 	return c.Internal.ChainHead(ctx)
 }
 
-func (c *FullNodeStruct) ChainGetRandomness(ctx context.Context, pts *types.TipSet, ticks []*types.Ticket, lb int) ([]byte, error) {
+func (c *FullNodeStruct) ChainGetRandomness(ctx context.Context, pts types.TipSetKey, ticks []*types.Ticket, lb int) ([]byte, error) {
 	return c.Internal.ChainGetRandomness(ctx, pts, ticks, lb)
 }
 
@@ -301,8 +301,8 @@ func (c *FullNodeStruct) ChainGetBlock(ctx context.Context, b cid.Cid) (*types.B
 	return c.Internal.ChainGetBlock(ctx, b)
 }
 
-func (c *FullNodeStruct) ChainGetTipSet(ctx context.Context, cids []cid.Cid) (*types.TipSet, error) {
-	return c.Internal.ChainGetTipSet(ctx, cids)
+func (c *FullNodeStruct) ChainGetTipSet(ctx context.Context, key types.TipSetKey) (*types.TipSet, error) {
+	return c.Internal.ChainGetTipSet(ctx, key)
 }
 
 func (c *FullNodeStruct) ChainGetBlockMessages(ctx context.Context, b cid.Cid) (*BlockMessages, error) {
diff --git a/chain/gen/gen.go b/chain/gen/gen.go
index fd0553f2d..1fa00f47f 100644
--- a/chain/gen/gen.go
+++ b/chain/gen/gen.go
@@ -354,7 +354,7 @@ func (cg *ChainGen) YieldRepo() (repo.Repo, error) {
 }
 
 type MiningCheckAPI interface {
-	ChainGetRandomness(context.Context, *types.TipSet, []*types.Ticket, int) ([]byte, error)
+	ChainGetRandomness(context.Context, types.TipSetKey, []*types.Ticket, int) ([]byte, error)
 
 	StateMinerPower(context.Context, address.Address, *types.TipSet) (api.MinerPower, error)
 
@@ -368,7 +368,7 @@ type mca struct {
 	sm *stmgr.StateManager
 }
 
-func (mca mca) ChainGetRandomness(ctx context.Context, pts *types.TipSet, ticks []*types.Ticket, lb int) ([]byte, error) {
+func (mca mca) ChainGetRandomness(ctx context.Context, pts types.TipSetKey, ticks []*types.Ticket, lb int) ([]byte, error) {
 	return mca.sm.ChainStore().GetRandomness(ctx, pts.Cids(), ticks, int64(lb))
 }
 
@@ -393,7 +393,7 @@ func (mca mca) WalletSign(ctx context.Context, a address.Address, v []byte) (*ty
 }
 
 func IsRoundWinner(ctx context.Context, ts *types.TipSet, ticks []*types.Ticket, miner address.Address, a MiningCheckAPI) (bool, types.ElectionProof, error) {
-	r, err := a.ChainGetRandomness(ctx, ts, ticks, build.EcRandomnessLookback)
+	r, err := a.ChainGetRandomness(ctx, ts.Key(), ticks, build.EcRandomnessLookback)
 	if err != nil {
 		return false, nil, xerrors.Errorf("chain get randomness: %w", err)
 	}
diff --git a/chain/types/tipset.go b/chain/types/tipset.go
index 733e29685..13fb7e582 100644
--- a/chain/types/tipset.go
+++ b/chain/types/tipset.go
@@ -123,6 +123,10 @@ func (ts *TipSet) Cids() []cid.Cid {
 	return ts.cids
 }
 
+func (ts *TipSet) Key() TipSetKey {
+	return NewTipSetKey(ts.cids...)
+}
+
 func (ts *TipSet) Height() uint64 {
 	return ts.height
 }
diff --git a/chain/types/tipset_key.go b/chain/types/tipset_key.go
new file mode 100644
index 000000000..34b1c8f18
--- /dev/null
+++ b/chain/types/tipset_key.go
@@ -0,0 +1,117 @@
+package types
+
+import (
+	"bytes"
+	"encoding/json"
+	"strings"
+
+	"github.com/ipfs/go-cid"
+	"github.com/multiformats/go-multihash"
+)
+
+// The length of a block header CID in bytes.
+var blockHeaderCIDLen int
+
+func init() {
+	c, err := cid.V1Builder{Codec: cid.DagCBOR, MhType: multihash.BLAKE2B_MIN + 31}.Sum([]byte{})
+	if err != nil {
+		panic(err)
+	}
+	blockHeaderCIDLen = len(c.Bytes())
+}
+
+// A TipSetKey is an immutable collection of CIDs forming a unique key for a tipset.
+// The CIDs are assumed to be distinct and in canonical order. Two keys with the same
+// CIDs in a different order are not considered equal.
+// TipSetKey is a lightweight value type, and may be compared for equality with ==.
+type TipSetKey struct {
+	// The internal representation is a concatenation of the bytes of the CIDs, which are
+	// self-describing, wrapped as a string.
+	// These gymnastics make the a TipSetKey usable as a map key.
+	// The empty key has value "".
+	value string
+}
+
+// NewTipSetKey builds a new key from a slice of CIDs.
+// The CIDs are assumed to be ordered correctly.
+func NewTipSetKey(cids ...cid.Cid) TipSetKey {
+	encoded := encodeKey(cids)
+	return TipSetKey{string(encoded)}
+}
+
+// TipSetKeyFromBytes wraps an encoded key, validating correct decoding.
+func TipSetKeyFromBytes(encoded []byte) (TipSetKey, error) {
+	_, err := decodeKey(encoded)
+	if err != nil {
+		return TipSetKey{}, err
+	}
+	return TipSetKey{string(encoded)}, nil
+}
+
+// Cids returns a slice of the CIDs comprising this key.
+func (k TipSetKey) Cids() []cid.Cid {
+	cids, err := decodeKey([]byte(k.value))
+	if err != nil {
+		panic("invalid tipset key: " + err.Error())
+	}
+	return cids
+}
+
+// String() returns a human-readable representation of the key.
+func (k TipSetKey) String() string {
+	b := strings.Builder{}
+	b.WriteString("{")
+	cids := k.Cids()
+	for i, c := range cids {
+		b.WriteString(c.String())
+		if i < len(cids)-1 {
+			b.WriteString(",")
+		}
+	}
+	b.WriteString("}")
+	return b.String()
+}
+
+// Bytes() returns a binary representation of the key.
+func (k TipSetKey) Bytes() []byte {
+	return []byte(k.value)
+}
+
+func (k *TipSetKey) MarshalJSON() ([]byte, error) {
+	return json.Marshal(k.Cids())
+}
+
+func (k *TipSetKey) UnmarshalJSON(b []byte) error {
+	var cids []cid.Cid
+	if err := json.Unmarshal(b, &cids); err != nil {
+		return err
+	}
+	k.value = string(encodeKey(cids))
+	return nil
+}
+
+func encodeKey(cids []cid.Cid) []byte {
+	buffer := new(bytes.Buffer)
+	for _, c := range cids {
+		// bytes.Buffer.Write() err is documented to be always nil.
+		_, _ = buffer.Write(c.Bytes())
+	}
+	return buffer.Bytes()
+}
+
+func decodeKey(encoded []byte) ([]cid.Cid, error) {
+	// To avoid reallocation of the underlying array, estimate the number of CIDs to be extracted
+	// by dividing the encoded length by the expected CID length.
+	estimatedCount := len(encoded) / blockHeaderCIDLen
+	cids := make([]cid.Cid, 0, estimatedCount)
+	nextIdx := 0
+	for nextIdx < len(encoded) {
+		nr, c, err := cid.CidFromBytes(encoded[nextIdx:])
+		if err != nil {
+			return nil, err
+		}
+		cids = append(cids, c)
+		nextIdx += nr
+	}
+	return cids, nil
+}
diff --git a/chain/types/tipset_key_test.go b/chain/types/tipset_key_test.go
new file mode 100644
index 000000000..c6411a741
--- /dev/null
+++ b/chain/types/tipset_key_test.go
@@ -0,0 +1,82 @@
+package types
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/ipfs/go-cid"
+	"github.com/multiformats/go-multihash"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestTipSetKey(t *testing.T) {
+	cb := cid.V1Builder{Codec: cid.DagCBOR, MhType: multihash.BLAKE2B_MIN+31}
+	c1, _ := cb.Sum([]byte("a"))
+	c2, _ := cb.Sum([]byte("b"))
+	c3, _ := cb.Sum([]byte("c"))
+	fmt.Println(len(c1.Bytes()))
+
+	t.Run("zero value", func(t *testing.T) {
+		assert.Equal(t, TipSetKey{}, NewTipSetKey())
+	})
+
+	t.Run("CID extraction", func(t *testing.T) {
+		assert.Equal(t, []cid.Cid{}, NewTipSetKey().Cids())
+		assert.Equal(t, []cid.Cid{c1}, NewTipSetKey(c1).Cids())
+		assert.Equal(t, []cid.Cid{c1, c2, c3}, NewTipSetKey(c1, c2, c3).Cids())
+
+		// The key doesn't check for duplicates.
+		assert.Equal(t, []cid.Cid{c1, c1}, NewTipSetKey(c1, c1).Cids())
+	})
+
+	t.Run("equality", func(t *testing.T) {
+		assert.Equal(t, NewTipSetKey(), NewTipSetKey())
+		assert.Equal(t, NewTipSetKey(c1), NewTipSetKey(c1))
+		assert.Equal(t, NewTipSetKey(c1, c2, c3), NewTipSetKey(c1, c2, c3))
+
+		assert.NotEqual(t, NewTipSetKey(), NewTipSetKey(c1))
+		assert.NotEqual(t, NewTipSetKey(c2), NewTipSetKey(c1))
+		// The key doesn't normalize order.
+		assert.NotEqual(t, NewTipSetKey(c1, c2), NewTipSetKey(c2, c1))
+	})
+
+	t.Run("encoding", func(t *testing.T) {
+		keys := []TipSetKey {
+			NewTipSetKey(),
+			NewTipSetKey(c1),
+			NewTipSetKey(c1, c2, c3),
+		}
+
+		for _, tk := range keys {
+			roundTrip, err := TipSetKeyFromBytes(tk.Bytes())
+			require.NoError(t, err)
+			assert.Equal(t, tk, roundTrip)
+		}
+
+		_, err := TipSetKeyFromBytes(NewTipSetKey(c1).Bytes()[1:])
+		assert.Error(t, err)
+	})
+
+	t.Run("JSON", func(t *testing.T) {
+		k0 := NewTipSetKey()
+		verifyJson(t, "[]", k0)
+		k3 := NewTipSetKey(c1, c2, c3)
+		verifyJson(t, `[` +
+			`{"/":"bafy2bzacecesrkxghscnq7vatble2hqdvwat6ed23vdu4vvo3uuggsoaya7ki"},` +
+			`{"/":"bafy2bzacebxfyh2fzoxrt6kcgc5dkaodpcstgwxxdizrww225vrhsizsfcg4g"},` +
+			`{"/":"bafy2bzacedwviarjtjraqakob5pslltmuo5n3xev3nt5zylezofkbbv5jclyu"}` +
+			`]`, k3)
+	})
+}
+
+func verifyJson(t *testing.T, expected string, k TipSetKey) {
+	bytes, err := k.MarshalJSON()
+	require.NoError(t, err)
+	assert.Equal(t, expected, string(bytes))
+
+	var rehydrated TipSetKey
+	err = rehydrated.UnmarshalJSON(bytes)
+	require.NoError(t, err)
+	assert.Equal(t, k, rehydrated)
+}
\ No newline at end of file
diff --git a/cli/chain.go b/cli/chain.go
index 0e948d36c..10c7dd5cc 100644
--- a/cli/chain.go
+++ b/cli/chain.go
@@ -319,7 +319,7 @@ var chainListCmd = &cli.Command{
 				break
 			}
 
-			head, err = api.ChainGetTipSet(ctx, head.Parents())
+			head, err = api.ChainGetTipSet(ctx, types.NewTipSetKey(head.Parents()...))
 			if err != nil {
 				return err
 			}
diff --git a/go.mod b/go.mod
index 116765150..8f3830386 100644
--- a/go.mod
+++ b/go.mod
@@ -27,7 +27,7 @@ require (
 	github.com/ipfs/go-block-format v0.0.2
 	github.com/ipfs/go-blockservice v0.1.3-0.20190908200855-f22eea50656c
 	github.com/ipfs/go-car v0.0.2
-	github.com/ipfs/go-cid v0.0.3
+	github.com/ipfs/go-cid v0.0.4-0.20191112011718-79e75dffeb10
 	github.com/ipfs/go-datastore v0.1.0
 	github.com/ipfs/go-ds-badger v0.0.5
 	github.com/ipfs/go-filestore v0.0.2
@@ -74,13 +74,13 @@ require (
 	github.com/mattn/go-runewidth v0.0.4 // indirect
 	github.com/miekg/dns v1.1.16 // indirect
 	github.com/minio/blake2b-simd v0.0.0-20160723061019-3f5f724cb5b1
-	github.com/minio/sha256-simd v0.1.0
+	github.com/minio/sha256-simd v0.1.1-0.20190913151208-6de447530771
 	github.com/mitchellh/go-homedir v1.1.0
 	github.com/multiformats/go-base32 v0.0.3
 	github.com/multiformats/go-multiaddr v0.0.4
 	github.com/multiformats/go-multiaddr-dns v0.0.3
 	github.com/multiformats/go-multiaddr-net v0.0.1
-	github.com/multiformats/go-multihash v0.0.7
+	github.com/multiformats/go-multihash v0.0.9
 	github.com/onsi/ginkgo v1.9.0 // indirect
 	github.com/onsi/gomega v1.6.0 // indirect
 	github.com/opentracing/opentracing-go v1.1.0
diff --git a/go.sum b/go.sum
index 71a254bd4..109f07c28 100644
--- a/go.sum
+++ b/go.sum
@@ -164,6 +164,8 @@ github.com/ipfs/go-cid v0.0.1/go.mod h1:GHWU/WuQdMPmIosc4Yn1bcCT7dSeX4lBafM7iqUP
 github.com/ipfs/go-cid v0.0.2/go.mod h1:GHWU/WuQdMPmIosc4Yn1bcCT7dSeX4lBafM7iqUPQvM=
 github.com/ipfs/go-cid v0.0.3 h1:UIAh32wymBpStoe83YCzwVQQ5Oy/H0FdxvUS6DJDzms=
 github.com/ipfs/go-cid v0.0.3/go.mod h1:GHWU/WuQdMPmIosc4Yn1bcCT7dSeX4lBafM7iqUPQvM=
+github.com/ipfs/go-cid v0.0.4-0.20191112011718-79e75dffeb10 h1:5mRf2p8Bv2iKiuPsGrQUrx38rdBm2T/03JCM6VWzoMc=
+github.com/ipfs/go-cid v0.0.4-0.20191112011718-79e75dffeb10/go.mod h1:/BYOuUoxkE+0f6tGzlzMvycuN+5l35VOR4Bpg2sCmds=
 github.com/ipfs/go-datastore v0.0.1/go.mod h1:d4KVXhMt913cLBEI/PXAy6ko+W7e9AhyAKBGh803qeE=
 github.com/ipfs/go-datastore v0.0.5/go.mod h1:d4KVXhMt913cLBEI/PXAy6ko+W7e9AhyAKBGh803qeE=
 github.com/ipfs/go-datastore v0.1.0 h1:TOxI04l8CmO4zGtesENhzm4PwkFwJXY3rKiYaaMf9fI=
@@ -432,6 +434,8 @@ github.com/minio/sha256-simd v0.0.0-20190131020904-2d45a736cd16/go.mod h1:2FMWW+
 github.com/minio/sha256-simd v0.0.0-20190328051042-05b4dd3047e5/go.mod h1:2FMWW+8GMoPweT6+pI63m9YE3Lmw4J71hV56Chs1E/U=
 github.com/minio/sha256-simd v0.1.0 h1:U41/2erhAKcmSI14xh/ZTUdBPOzDOIfS93ibzUSl8KM=
 github.com/minio/sha256-simd v0.1.0/go.mod h1:2FMWW+8GMoPweT6+pI63m9YE3Lmw4J71hV56Chs1E/U=
+github.com/minio/sha256-simd v0.1.1-0.20190913151208-6de447530771 h1:MHkK1uRtFbVqvAgvWxafZe54+5uBxLluGylDiKgdhwo=
+github.com/minio/sha256-simd v0.1.1-0.20190913151208-6de447530771/go.mod h1:B5e1o+1/KgNmWrSQK08Y6Z1Vb5pwIktudl0J58iy0KM=
 github.com/mitchellh/go-homedir v1.1.0 h1:lukF9ziXFxDFPkA1vsr5zpc1XuPDn/wFntq5mG+4E0Y=
 github.com/mitchellh/go-homedir v1.1.0/go.mod h1:SfyaCUpYCn1Vlf4IUYiD9fPX4A5wJrkLzIz1N1q0pr0=
 github.com/mitchellh/mapstructure v1.1.2/go.mod h1:FVVH3fgwuzCH5S8UJGiWEs2h04kUh9fWfEaFds41c1Y=
@@ -457,8 +461,8 @@ github.com/multiformats/go-multibase v0.0.1 h1:PN9/v21eLywrFWdFNsFKaU04kLJzuYzmr
 github.com/multiformats/go-multibase v0.0.1/go.mod h1:bja2MqRZ3ggyXtZSEDKpl0uO/gviWFaSteVbWT51qgs=
 github.com/multiformats/go-multihash v0.0.1/go.mod h1:w/5tugSrLEbWqlcgJabL3oHFKTwfvkofsjW2Qa1ct4U=
 github.com/multiformats/go-multihash v0.0.5/go.mod h1:lt/HCbqlQwlPBz7lv0sQCdtfcMtlJvakRUn/0Ual8po=
-github.com/multiformats/go-multihash v0.0.7 h1:uoqoE03rGJdlQEPq2EAc6UeSbo4L7mZyeAAoqNalf54=
-github.com/multiformats/go-multihash v0.0.7/go.mod h1:XuKXPp8VHcTygube3OWZC+aZrA+H1IhmjoCDtJc7PXM=
+github.com/multiformats/go-multihash v0.0.9 h1:aoijQXYYl7Xtb2pUUP68R+ys1TlnlR3eX6wmozr0Hp4=
+github.com/multiformats/go-multihash v0.0.9/go.mod h1:YSLudS+Pi8NHE7o6tb3D8vrpKa63epEDmG8nTduyAew=
 github.com/multiformats/go-multistream v0.0.1/go.mod h1:fJTiDfXJVmItycydCnNx4+wSzZ5NwG2FEVAI30fiovg=
 github.com/multiformats/go-multistream v0.1.0 h1:UpO6jrsjqs46mqAK3n6wKRYFhugss9ArzbyUzU+4wkQ=
 github.com/multiformats/go-multistream v0.1.0/go.mod h1:fJTiDfXJVmItycydCnNx4+wSzZ5NwG2FEVAI30fiovg=
diff --git a/node/impl/full/chain.go b/node/impl/full/chain.go
index fd3a91d66..4285682fc 100644
--- a/node/impl/full/chain.go
+++ b/node/impl/full/chain.go
@@ -28,7 +28,7 @@ func (a *ChainAPI) ChainHead(context.Context) (*types.TipSet, error) {
 	return a.Chain.GetHeaviestTipSet(), nil
 }
 
-func (a *ChainAPI) ChainGetRandomness(ctx context.Context, pts *types.TipSet, tickets []*types.Ticket, lb int) ([]byte, error) {
+func (a *ChainAPI) ChainGetRandomness(ctx context.Context, pts types.TipSetKey, tickets []*types.Ticket, lb int) ([]byte, error) {
 	return a.Chain.GetRandomness(ctx, pts.Cids(), tickets, int64(lb))
 }
 
@@ -36,8 +36,8 @@ func (a *ChainAPI) ChainGetBlock(ctx context.Context, msg cid.Cid) (*types.Block
 	return a.Chain.GetBlock(msg)
 }
 
-func (a *ChainAPI) ChainGetTipSet(ctx context.Context, cids []cid.Cid) (*types.TipSet, error) {
-	return a.Chain.LoadTipSet(cids)
+func (a *ChainAPI) ChainGetTipSet(ctx context.Context, key types.TipSetKey) (*types.TipSet, error) {
+	return a.Chain.LoadTipSet(key.Cids())
 }
 
 func (a *ChainAPI) ChainGetBlockMessages(ctx context.Context, msg cid.Cid) (*api.BlockMessages, error) {
diff --git a/node/modules/storageminer.go b/node/modules/storageminer.go
index 6812a7f35..e5cbe8d62 100644
--- a/node/modules/storageminer.go
+++ b/node/modules/storageminer.go
@@ -221,7 +221,7 @@ func SealTicketGen(api api.FullNode) storage.TicketFn {
 			return nil, xerrors.Errorf("getting head ts for SealTicket failed: %w", err)
 		}
 
-		r, err := api.ChainGetRandomness(ctx, ts, nil, build.SealRandomnessLookback)
+		r, err := api.ChainGetRandomness(ctx, ts.Key(), nil, build.SealRandomnessLookback)
 		if err != nil {
 			return nil, xerrors.Errorf("getting randomness for SealTicket failed: %w", err)
 		}
diff --git a/storage/miner.go b/storage/miner.go
index 5cc8d37ed..af8bf5a6d 100644
--- a/storage/miner.go
+++ b/storage/miner.go
@@ -64,7 +64,7 @@ type storageMinerApi interface {
 
 	ChainHead(context.Context) (*types.TipSet, error)
 	ChainNotify(context.Context) (<-chan []*store.HeadChange, error)
-	ChainGetRandomness(context.Context, *types.TipSet, []*types.Ticket, int) ([]byte, error)
+	ChainGetRandomness(context.Context, types.TipSetKey, []*types.Ticket, int) ([]byte, error)
 	ChainGetTipSetByHeight(context.Context, uint64, *types.TipSet) (*types.TipSet, error)
 	ChainGetBlockMessages(context.Context, cid.Cid) (*api.BlockMessages, error)
 
diff --git a/storage/post.go b/storage/post.go
index 98bd798fc..ab94d719a 100644
--- a/storage/post.go
+++ b/storage/post.go
@@ -156,7 +156,7 @@ func (p *post) preparePost(ctx context.Context) error {
 
 	// Compute how many blocks back we have to look from the given tipset for the PoSt challenge
 	challengeLookback := int((int64(p.ts.Height()) - int64(p.ppe)) + int64(build.PoStChallangeTime) + int64(build.PoStRandomnessLookback))
-	r, err := p.m.api.ChainGetRandomness(ctx, p.ts, nil, challengeLookback)
+	r, err := p.m.api.ChainGetRandomness(ctx, p.ts.Key(), nil, challengeLookback)
 	if err != nil {
 		return xerrors.Errorf("failed to get chain randomness for post (ts=%d; ppe=%d): %w", p.ts.Height(), p.ppe, err)
 	}
diff --git a/storage/sector_states.go b/storage/sector_states.go
index d91e3cead..2e69b7ce7 100644
--- a/storage/sector_states.go
+++ b/storage/sector_states.go
@@ -145,7 +145,7 @@ func (m *Miner) preCommitted(ctx context.Context, sector SectorInfo) (func(*Sect
 	log.Infof("precommit for sector %d made it on chain, will start proof computation at height %d", sector.SectorID, randHeight)
 
 	err = m.events.ChainAt(func(ctx context.Context, ts *types.TipSet, curH uint64) error {
-		rand, err := m.api.ChainGetRandomness(ctx, ts, nil, int(ts.Height()-randHeight))
+		rand, err := m.api.ChainGetRandomness(ctx, ts.Key(), nil, int(ts.Height()-randHeight))
 		if err != nil {
 			return xerrors.Errorf("failed to get randomness for computing seal proof: %w", err)
 		}