diff --git a/db/c_level_db.go b/db/c_level_db.go
index 7910628bf..f1a5a3aef 100644
--- a/db/c_level_db.go
+++ b/db/c_level_db.go
@@ -50,6 +50,7 @@ func NewCLevelDB(name string, dir string) (*CLevelDB, error) {
 	return database, nil
 }
 
+// Implements DB.
 func (db *CLevelDB) Get(key []byte) []byte {
 	key = nonNilBytes(key)
 	res, err := db.db.Get(db.ro, key)
@@ -59,10 +60,12 @@ func (db *CLevelDB) Get(key []byte) []byte {
 	return res
 }
 
+// Implements DB.
 func (db *CLevelDB) Has(key []byte) bool {
 	return db.Get(key) != nil
 }
 
+// Implements DB.
 func (db *CLevelDB) Set(key []byte, value []byte) {
 	key = nonNilBytes(key)
 	value = nonNilBytes(value)
@@ -72,6 +75,7 @@ func (db *CLevelDB) Set(key []byte, value []byte) {
 	}
 }
 
+// Implements DB.
 func (db *CLevelDB) SetSync(key []byte, value []byte) {
 	key = nonNilBytes(key)
 	value = nonNilBytes(value)
@@ -81,6 +85,7 @@ func (db *CLevelDB) SetSync(key []byte, value []byte) {
 	}
 }
 
+// Implements DB.
 func (db *CLevelDB) Delete(key []byte) {
 	key = nonNilBytes(key)
 	err := db.db.Delete(db.wo, key)
@@ -89,6 +94,7 @@ func (db *CLevelDB) Delete(key []byte) {
 	}
 }
 
+// Implements DB.
 func (db *CLevelDB) DeleteSync(key []byte) {
 	key = nonNilBytes(key)
 	err := db.db.Delete(db.woSync, key)
@@ -101,6 +107,7 @@ func (db *CLevelDB) DB() *levigo.DB {
 	return db.db
 }
 
+// Implements DB.
 func (db *CLevelDB) Close() {
 	db.db.Close()
 	db.ro.Close()
@@ -108,6 +115,7 @@ func (db *CLevelDB) Close() {
 	db.woSync.Close()
 }
 
+// Implements DB.
 func (db *CLevelDB) Print() {
 	itr := db.Iterator(nil, nil)
 	defer itr.Close()
@@ -118,6 +126,7 @@ func (db *CLevelDB) Print() {
 	}
 }
 
+// Implements DB.
 func (db *CLevelDB) Stats() map[string]string {
 	// TODO: Find the available properties for the C LevelDB implementation
 	keys := []string{}
@@ -133,6 +142,7 @@ func (db *CLevelDB) Stats() map[string]string {
 //----------------------------------------
 // Batch
 
+// Implements DB.
 func (db *CLevelDB) NewBatch() Batch {
 	batch := levigo.NewWriteBatch()
 	return &cLevelDBBatch{db, batch}
@@ -143,14 +153,17 @@ type cLevelDBBatch struct {
 	batch *levigo.WriteBatch
 }
 
+// Implements Batch.
 func (mBatch *cLevelDBBatch) Set(key, value []byte) {
 	mBatch.batch.Put(key, value)
 }
 
+// Implements Batch.
 func (mBatch *cLevelDBBatch) Delete(key []byte) {
 	mBatch.batch.Delete(key)
 }
 
+// Implements Batch.
 func (mBatch *cLevelDBBatch) Write() {
 	err := mBatch.db.db.Write(mBatch.db.wo, mBatch.batch)
 	if err != nil {
@@ -204,7 +217,7 @@ func (itr cLevelDBIterator) Domain() ([]byte, []byte) {
 }
 
 func (itr cLevelDBIterator) Valid() bool {
-  
+
 	// Once invalid, forever invalid.
 	if itr.isInvalid {
 		return false
diff --git a/db/db.go b/db/db.go
index b43b06554..25ff93ec5 100644
--- a/db/db.go
+++ b/db/db.go
@@ -2,7 +2,7 @@ package db
 
 import "fmt"
 
-//-----------------------------------------------------------------------------
+//----------------------------------------
 // Main entry
 
 const (
diff --git a/db/go_level_db.go b/db/go_level_db.go
index bf2b3bf76..7d60e060f 100644
--- a/db/go_level_db.go
+++ b/db/go_level_db.go
@@ -39,6 +39,7 @@ func NewGoLevelDB(name string, dir string) (*GoLevelDB, error) {
 	return database, nil
 }
 
+// Implements DB.
 func (db *GoLevelDB) Get(key []byte) []byte {
 	key = nonNilBytes(key)
 	res, err := db.db.Get(key, nil)
@@ -52,10 +53,12 @@ func (db *GoLevelDB) Get(key []byte) []byte {
 	return res
 }
 
+// Implements DB.
 func (db *GoLevelDB) Has(key []byte) bool {
 	return db.Get(key) != nil
 }
 
+// Implements DB.
 func (db *GoLevelDB) Set(key []byte, value []byte) {
 	key = nonNilBytes(key)
 	value = nonNilBytes(value)
@@ -65,6 +68,7 @@ func (db *GoLevelDB) Set(key []byte, value []byte) {
 	}
 }
 
+// Implements DB.
 func (db *GoLevelDB) SetSync(key []byte, value []byte) {
 	key = nonNilBytes(key)
 	value = nonNilBytes(value)
@@ -74,6 +78,7 @@ func (db *GoLevelDB) SetSync(key []byte, value []byte) {
 	}
 }
 
+// Implements DB.
 func (db *GoLevelDB) Delete(key []byte) {
 	key = nonNilBytes(key)
 	err := db.db.Delete(key, nil)
@@ -82,6 +87,7 @@ func (db *GoLevelDB) Delete(key []byte) {
 	}
 }
 
+// Implements DB.
 func (db *GoLevelDB) DeleteSync(key []byte) {
 	key = nonNilBytes(key)
 	err := db.db.Delete(key, &opt.WriteOptions{Sync: true})
@@ -94,10 +100,12 @@ func (db *GoLevelDB) DB() *leveldb.DB {
 	return db.db
 }
 
+// Implements DB.
 func (db *GoLevelDB) Close() {
 	db.db.Close()
 }
 
+// Implements DB.
 func (db *GoLevelDB) Print() {
 	str, _ := db.db.GetProperty("leveldb.stats")
 	fmt.Printf("%v\n", str)
@@ -110,6 +118,7 @@ func (db *GoLevelDB) Print() {
 	}
 }
 
+// Implements DB.
 func (db *GoLevelDB) Stats() map[string]string {
 	keys := []string{
 		"leveldb.num-files-at-level{n}",
@@ -135,6 +144,7 @@ func (db *GoLevelDB) Stats() map[string]string {
 //----------------------------------------
 // Batch
 
+// Implements DB.
 func (db *GoLevelDB) NewBatch() Batch {
 	batch := new(leveldb.Batch)
 	return &goLevelDBBatch{db, batch}
@@ -145,18 +155,21 @@ type goLevelDBBatch struct {
 	batch *leveldb.Batch
 }
 
+// Implements Batch.
 func (mBatch *goLevelDBBatch) Set(key, value []byte) {
 	mBatch.batch.Put(key, value)
 }
 
+// Implements Batch.
 func (mBatch *goLevelDBBatch) Delete(key []byte) {
 	mBatch.batch.Delete(key)
 }
 
+// Implements Batch.
 func (mBatch *goLevelDBBatch) Write() {
 	err := mBatch.db.db.Write(mBatch.batch, nil)
 	if err != nil {
-		PanicCrisis(err)
+		panic(err)
 	}
 }
 
@@ -165,6 +178,17 @@ func (mBatch *goLevelDBBatch) Write() {
 // NOTE This is almost identical to db/c_level_db.Iterator
 // Before creating a third version, refactor.
 
+// Implements DB.
+func (db *GoLevelDB) Iterator(start, end []byte) Iterator {
+	itr := db.db.NewIterator(nil, nil)
+	return newGoLevelDBIterator(itr, start, end, false)
+}
+
+// Implements DB.
+func (db *GoLevelDB) ReverseIterator(start, end []byte) Iterator {
+	panic("not implemented yet") // XXX
+}
+
 type goLevelDBIterator struct {
 	source    iterator.Iterator
 	start     []byte
@@ -189,19 +213,12 @@ func newGoLevelDBIterator(source iterator.Iterator, start, end []byte, isReverse
 	}
 }
 
-func (db *GoLevelDB) Iterator(start, end []byte) Iterator {
-	itr := db.db.NewIterator(nil, nil)
-	return newGoLevelDBIterator(itr, start, end, false)
-}
-
-func (db *GoLevelDB) ReverseIterator(start, end []byte) Iterator {
-	panic("not implemented yet") // XXX
-}
-
+// Implements Iterator.
 func (itr *goLevelDBIterator) Domain() ([]byte, []byte) {
 	return itr.start, itr.end
 }
 
+// Implements Iterator.
 func (itr *goLevelDBIterator) Valid() bool {
 
 	// Once invalid, forever invalid.
@@ -230,24 +247,32 @@ func (itr *goLevelDBIterator) Valid() bool {
 	return true
 }
 
+// Implements Iterator.
 func (itr *goLevelDBIterator) Key() []byte {
+	// Key returns a copy of the current key.
+	// See https://github.com/syndtr/goleveldb/blob/52c212e6c196a1404ea59592d3f1c227c9f034b2/leveldb/iterator/iter.go#L88
 	itr.assertNoError()
 	itr.assertIsValid()
-	return itr.source.Key()
+	return cp(itr.source.Key())
 }
 
+// Implements Iterator.
 func (itr *goLevelDBIterator) Value() []byte {
+	// Value returns a copy of the current value.
+	// See https://github.com/syndtr/goleveldb/blob/52c212e6c196a1404ea59592d3f1c227c9f034b2/leveldb/iterator/iter.go#L88
 	itr.assertNoError()
 	itr.assertIsValid()
-	return itr.source.Value()
+	return cp(itr.source.Value())
 }
 
+// Implements Iterator.
 func (itr *goLevelDBIterator) Next() {
 	itr.assertNoError()
 	itr.assertIsValid()
 	itr.source.Next()
 }
 
+// Implements Iterator.
 func (itr *goLevelDBIterator) Close() {
 	itr.source.Release()
 }
diff --git a/db/mem_db.go b/db/mem_db.go
index e2470d7f2..1e3bee5a5 100644
--- a/db/mem_db.go
+++ b/db/mem_db.go
@@ -26,14 +26,16 @@ func NewMemDB() *MemDB {
 	return database
 }
 
+// Implements DB.
 func (db *MemDB) Get(key []byte) []byte {
 	db.mtx.Lock()
 	defer db.mtx.Unlock()
 	key = nonNilBytes(key)
-  
+
 	return db.db[string(key)]
 }
 
+// Implements DB.
 func (db *MemDB) Has(key []byte) bool {
 	db.mtx.Lock()
 	defer db.mtx.Unlock()
@@ -43,6 +45,7 @@ func (db *MemDB) Has(key []byte) bool {
 	return ok
 }
 
+// Implements DB.
 func (db *MemDB) Set(key []byte, value []byte) {
 	db.mtx.Lock()
 	defer db.mtx.Unlock()
@@ -50,6 +53,7 @@ func (db *MemDB) Set(key []byte, value []byte) {
 	db.SetNoLock(key, value)
 }
 
+// Implements DB.
 func (db *MemDB) SetSync(key []byte, value []byte) {
 	db.mtx.Lock()
 	defer db.mtx.Unlock()
@@ -57,7 +61,7 @@ func (db *MemDB) SetSync(key []byte, value []byte) {
 	db.SetNoLock(key, value)
 }
 
-// NOTE: Implements atomicSetDeleter
+// Implements atomicSetDeleter.
 func (db *MemDB) SetNoLock(key []byte, value []byte) {
 	key = nonNilBytes(key)
 	value = nonNilBytes(value)
@@ -65,6 +69,7 @@ func (db *MemDB) SetNoLock(key []byte, value []byte) {
 	db.db[string(key)] = value
 }
 
+// Implements DB.
 func (db *MemDB) Delete(key []byte) {
 	db.mtx.Lock()
 	defer db.mtx.Unlock()
@@ -72,6 +77,7 @@ func (db *MemDB) Delete(key []byte) {
 	db.DeleteNoLock(key)
 }
 
+// Implements DB.
 func (db *MemDB) DeleteSync(key []byte) {
 	db.mtx.Lock()
 	defer db.mtx.Unlock()
@@ -79,13 +85,14 @@ func (db *MemDB) DeleteSync(key []byte) {
 	db.DeleteNoLock(key)
 }
 
-// NOTE: Implements atomicSetDeleter
+// Implements atomicSetDeleter.
 func (db *MemDB) DeleteNoLock(key []byte) {
 	key = nonNilBytes(key)
 
 	delete(db.db, string(key))
 }
 
+// Implements DB.
 func (db *MemDB) Close() {
 	// Close is a noop since for an in-memory
 	// database, we don't have a destination
@@ -94,6 +101,7 @@ func (db *MemDB) Close() {
 	// See the discussion in https://github.com/tendermint/tmlibs/pull/56
 }
 
+// Implements DB.
 func (db *MemDB) Print() {
 	db.mtx.Lock()
 	defer db.mtx.Unlock()
@@ -103,6 +111,7 @@ func (db *MemDB) Print() {
 	}
 }
 
+// Implements DB.
 func (db *MemDB) Stats() map[string]string {
 	db.mtx.Lock()
 	defer db.mtx.Unlock()
@@ -113,6 +122,10 @@ func (db *MemDB) Stats() map[string]string {
 	return stats
 }
 
+//----------------------------------------
+// Batch
+
+// Implements DB.
 func (db *MemDB) NewBatch() Batch {
 	db.mtx.Lock()
 	defer db.mtx.Unlock()
@@ -125,7 +138,9 @@ func (db *MemDB) Mutex() *sync.Mutex {
 }
 
 //----------------------------------------
+// Iterator
 
+// Implements DB.
 func (db *MemDB) Iterator(start, end []byte) Iterator {
 	db.mtx.Lock()
 	defer db.mtx.Unlock()
@@ -134,6 +149,7 @@ func (db *MemDB) Iterator(start, end []byte) Iterator {
 	return newMemDBIterator(db, keys, start, end)
 }
 
+// Implements DB.
 func (db *MemDB) ReverseIterator(start, end []byte) Iterator {
 	db.mtx.Lock()
 	defer db.mtx.Unlock()
@@ -142,25 +158,6 @@ func (db *MemDB) ReverseIterator(start, end []byte) Iterator {
 	return newMemDBIterator(db, keys, start, end)
 }
 
-func (db *MemDB) getSortedKeys(start, end []byte, reverse bool) []string {
-	keys := []string{}
-	for key, _ := range db.db {
-		if IsKeyInDomain([]byte(key), start, end, false) {
-			keys = append(keys, key)
-		}
-	}
-	sort.Strings(keys)
-	if reverse {
-		nkeys := len(keys)
-		for i := 0; i < nkeys/2; i++ {
-			keys[i] = keys[nkeys-i-1]
-		}
-	}
-	return keys
-}
-
-var _ Iterator = (*memDBIterator)(nil)
-
 // We need a copy of all of the keys.
 // Not the best, but probably not a bottleneck depending.
 type memDBIterator struct {
@@ -171,6 +168,8 @@ type memDBIterator struct {
 	end   []byte
 }
 
+var _ Iterator = (*memDBIterator)(nil)
+
 // Keys is expected to be in reverse order for reverse iterators.
 func newMemDBIterator(db DB, keys []string, start, end []byte) *memDBIterator {
 	return &memDBIterator{
@@ -182,30 +181,36 @@ func newMemDBIterator(db DB, keys []string, start, end []byte) *memDBIterator {
 	}
 }
 
+// Implements Iterator.
 func (itr *memDBIterator) Domain() ([]byte, []byte) {
 	return itr.start, itr.end
 }
 
+// Implements Iterator.
 func (itr *memDBIterator) Valid() bool {
 	return 0 <= itr.cur && itr.cur < len(itr.keys)
 }
 
+// Implements Iterator.
 func (itr *memDBIterator) Next() {
 	itr.assertIsValid()
 	itr.cur++
 }
 
+// Implements Iterator.
 func (itr *memDBIterator) Key() []byte {
 	itr.assertIsValid()
 	return []byte(itr.keys[itr.cur])
 }
 
+// Implements Iterator.
 func (itr *memDBIterator) Value() []byte {
 	itr.assertIsValid()
 	key := []byte(itr.keys[itr.cur])
 	return itr.db.Get(key)
 }
 
+// Implements Iterator.
 func (itr *memDBIterator) Close() {
 	itr.keys = nil
 	itr.db = nil
@@ -215,4 +220,24 @@ func (itr *memDBIterator) assertIsValid() {
 	if !itr.Valid() {
 		panic("memDBIterator is invalid")
 	}
-}
\ No newline at end of file
+}
+
+//----------------------------------------
+// Misc.
+
+func (db *MemDB) getSortedKeys(start, end []byte, reverse bool) []string {
+	keys := []string{}
+	for key, _ := range db.db {
+		if IsKeyInDomain([]byte(key), start, end, false) {
+			keys = append(keys, key)
+		}
+	}
+	sort.Strings(keys)
+	if reverse {
+		nkeys := len(keys)
+		for i := 0; i < nkeys/2; i++ {
+			keys[i] = keys[nkeys-i-1]
+		}
+	}
+	return keys
+}
diff --git a/db/types.go b/db/types.go
index 6e5d2408d..07858087a 100644
--- a/db/types.go
+++ b/db/types.go
@@ -4,19 +4,23 @@ type DB interface {
 
 	// Get returns nil iff key doesn't exist.
 	// A nil key is interpreted as an empty byteslice.
+	// CONTRACT: key, value readonly []byte
 	Get([]byte) []byte
 
 	// Has checks if a key exists.
 	// A nil key is interpreted as an empty byteslice.
+	// CONTRACT: key, value readonly []byte
 	Has(key []byte) bool
 
 	// Set sets the key.
 	// A nil key is interpreted as an empty byteslice.
+	// CONTRACT: key, value readonly []byte
 	Set([]byte, []byte)
 	SetSync([]byte, []byte)
 
 	// Delete deletes the key.
 	// A nil key is interpreted as an empty byteslice.
+	// CONTRACT: key readonly []byte
 	Delete([]byte)
 	DeleteSync([]byte)
 
@@ -25,6 +29,7 @@ type DB interface {
 	// A nil start is interpreted as an empty byteslice.
 	// If end is nil, iterates up to the last item (inclusive).
 	// CONTRACT: No writes may happen within a domain while an iterator exists over it.
+	// CONTRACT: start, end readonly []byte
 	Iterator(start, end []byte) Iterator
 
 	// Iterate over a domain of keys in descending order. End is exclusive.
@@ -32,6 +37,7 @@ type DB interface {
 	// If start is nil, iterates from the last/greatest item (inclusive).
 	// If end is nil, iterates up to the first/least item (iclusive).
 	// CONTRACT: No writes may happen within a domain while an iterator exists over it.
+	// CONTRACT: start, end readonly []byte
 	ReverseIterator(start, end []byte) Iterator
 
 	// Closes the connection.
@@ -56,11 +62,12 @@ type Batch interface {
 }
 
 type SetDeleter interface {
-	Set(key, value []byte)
-	Delete(key []byte)
+	Set(key, value []byte) // CONTRACT: key, value readonly []byte
+	Delete(key []byte)     // CONTRACT: key readonly []byte
 }
 
 //----------------------------------------
+// Iterator
 
 /*
 	Usage:
@@ -83,6 +90,7 @@ type Iterator interface {
 	//
 	// The smallest key is the empty byte array []byte{} - see BeginningKey().
 	// The largest key is the nil byte array []byte(nil) - see EndingKey().
+	// CONTRACT: start, end readonly []byte
 	Domain() (start []byte, end []byte)
 
 	// Valid returns whether the current position is valid.
@@ -96,14 +104,14 @@ type Iterator interface {
 	Next()
 
 	// Key returns the key of the cursor.
-	//
 	// If Valid returns false, this method will panic.
-	Key() []byte
+	// CONTRACT: key readonly []byte
+	Key() (key []byte)
 
 	// Value returns the value of the cursor.
-	//
 	// If Valid returns false, this method will panic.
-	Value() []byte
+	// CONTRACT: value readonly []byte
+	Value() (value []byte)
 
 	// Close releases the Iterator.
 	Close()
diff --git a/glide.lock b/glide.lock
index 83c8551e0..146a32a0f 100644
--- a/glide.lock
+++ b/glide.lock
@@ -1,10 +1,10 @@
 hash: 325b2f9c7e84696f88fa88126a22eb1e1e91c2be5f60402d17bfaad6713b33c2
-updated: 2017-12-25T17:45:52.357002873-08:00
+updated: 2017-12-28T18:27:21.247160207-08:00
 imports:
 - name: github.com/fsnotify/fsnotify
   version: 4da3e2cfbabc9f751898f250b49f2439785783a1
 - name: github.com/go-kit/kit
-  version: e3b2152e0063c5f05efea89ecbe297852af2a92d
+  version: e2b298466b32c7cd5579a9b9b07e968fc9d9452c
   subpackages:
   - log
   - log/level
@@ -12,7 +12,13 @@ imports:
 - name: github.com/go-logfmt/logfmt
   version: 390ab7935ee28ec6b286364bba9b4dd6410cb3d5
 - name: github.com/go-stack/stack
-  version: 259ab82a6cad3992b4e21ff5cac294ccb06474bc
+  version: 817915b46b97fd7bb80e8ab6b69f01a53ac3eebf
+- name: github.com/gogo/protobuf
+  version: 342cbe0a04158f6dcb03ca0079991a51a4248c02
+  subpackages:
+  - gogoproto
+  - proto
+  - protoc-gen-gogo/descriptor
 - name: github.com/golang/snappy
   version: 553a641470496b2327abcac10b36396bd98e45c9
 - name: github.com/hashicorp/hcl
@@ -45,7 +51,7 @@ imports:
 - name: github.com/pelletier/go-toml
   version: 13d49d4606eb801b8f01ae542b4afc4c6ee3d84a
 - name: github.com/pkg/errors
-  version: f15c970de5b76fac0b59abb32d62c17cc7bed265
+  version: 645ef00459ed84a119197bfb8d8205042c6df63d
 - name: github.com/spf13/afero
   version: 5660eeed305fe5f69c8fc6cf899132a459a97064
   subpackages:
@@ -57,11 +63,11 @@ imports:
 - name: github.com/spf13/jwalterweatherman
   version: 12bd96e66386c1960ab0f74ced1362f66f552f7b
 - name: github.com/spf13/pflag
-  version: 4c012f6dcd9546820e378d0bdda4d8fc772cdfea
+  version: 97afa5e7ca8a08a383cb259e06636b5e2cc7897f
 - name: github.com/spf13/viper
   version: 8ef37cbca71638bf32f3d5e194117d4cb46da163
 - name: github.com/syndtr/goleveldb
-  version: adf24ef3f94bd13ec4163060b21a5678f22b429b
+  version: b89cc31ef7977104127d34c1bd31ebd1a9db2199
   subpackages:
   - leveldb
   - leveldb/cache
@@ -76,7 +82,7 @@ imports:
   - leveldb/table
   - leveldb/util
 - name: github.com/tendermint/go-wire
-  version: 5ab49b4c6ad674da6b81442911cf713ef0afb544
+  version: 27be46e25124ddf775e23317a83647ce62a93f6b
   subpackages:
   - data
   - data/base58
@@ -85,7 +91,7 @@ imports:
   subpackages:
   - term
 - name: golang.org/x/crypto
-  version: 94eea52f7b742c7cbe0b03b22f0c4c8631ece122
+  version: edd5e9b0879d13ee6970a50153d85b8fec9f7686
   subpackages:
   - ripemd160
 - name: golang.org/x/sys
@@ -93,7 +99,7 @@ imports:
   subpackages:
   - unix
 - name: golang.org/x/text
-  version: 75cc3cad82b5f47d3fb229ddda8c5167da14f294
+  version: c01e4764d870b77f8abe5096ee19ad20d80e8075
   subpackages:
   - transform
   - unicode/norm