diff --git a/mcrypto/mcrypto.go b/mcrypto/mcrypto.go
index 3e64660..0c18d2d 100644
--- a/mcrypto/mcrypto.go
+++ b/mcrypto/mcrypto.go
@@ -2,3 +2,42 @@
 // cryptography, notably related to unique identifiers, signing/verifying data,
 // and encrypting/decrypting data
 package mcrypto
+
+import (
+	"bytes"
+	"encoding/hex"
+	"fmt"
+	"io"
+	"strconv"
+	"strings"
+)
+
+// Instead of outputing opaque hex garbage, this package opts to add a prefix to
+// the garbage. Each "type" of string returned has its own character which is
+// not found in the hex range (0-9, a-f), and in addition each also has a
+// version character prefixed as well, in case something wants to be changed
+// going forward.
+//
+// We keep the constant prefices here to ensure there's no conflicts across
+// string types in this package.
+const (
+	uuidV0      = "0u" // u for uuid
+	sigV0       = "0s" // s for signature
+	exSigV0     = "0t" // t for time
+	uniqueSigV0 = "0q" // q for uni"q"ue
+	encryptedV0 = "0n" // n for "n"-crypted, harharhar
+)
+
+func stripPrefix(s, prefix string) (string, bool) {
+	trimmed := strings.TrimPrefix(s, prefix)
+	return trimmed, len(trimmed) < len(s)
+}
+
+func prefixReader(r io.Reader, prefix []byte) io.Reader {
+	b := make([]byte, 0, len(prefix)+hex.EncodedLen(strconv.IntSize)+2)
+	buf := bytes.NewBuffer(b)
+	fmt.Fprintf(buf, "%x\n", len(prefix))
+	buf.Write(prefix)
+	buf.WriteByte('\n')
+	return io.MultiReader(buf, r)
+}
diff --git a/mcrypto/sig.go b/mcrypto/sig.go
new file mode 100644
index 0000000..4e8331c
--- /dev/null
+++ b/mcrypto/sig.go
@@ -0,0 +1,267 @@
+package mcrypto
+
+import (
+	"bytes"
+	"crypto/hmac"
+	"crypto/rand"
+	"crypto/sha256"
+	"encoding/binary"
+	"encoding/hex"
+	"errors"
+	"hash"
+	"io"
+	"strings"
+	"time"
+
+	"github.com/mediocregopher/mediocre-go-lib/mlog"
+)
+
+var (
+	errMalformedSig = errors.New("malformed signature")
+
+	// ErrInvalidSig is returned by Signer related functions when an invalid
+	// signature is used, e.g. it is a signature for different data, or uses a
+	// different secret key, or has expired
+	ErrInvalidSig = errors.New("invalid signature")
+)
+
+// Signer is some entity which can generate signatures for arbitrary data and
+// can later verify those signatures
+type Signer interface {
+	sign(io.Reader) (string, error)
+
+	// returns an error if io.Reader returns one ever, or if the signature
+	// couldn't be verified
+	verify(string, io.Reader) error
+}
+
+// Sign reads all data from the io.Reader and signs it using the given Signer
+func Sign(s Signer, r io.Reader) (string, error) {
+	return s.sign(r)
+}
+
+// SignBytes uses the Signer to generate a signature for the given []bytes
+func SignBytes(s Signer, b []byte) string {
+	sig, err := s.sign(bytes.NewBuffer(b))
+	if err != nil {
+		panic(err)
+	}
+	return sig
+}
+
+// SignString uses the Signer to generate a signature for the given string
+func SignString(s Signer, in string) string {
+	return SignBytes(s, []byte(in))
+}
+
+// Verify reads all data from the io.Reader and uses the Signer to verify that
+// the signature is for that data.
+//
+// Returns any errors from io.Reader, or ErrInvalidSig (use merry.Is(err,
+// mcrypto.ErrInvalidSig) to check).
+func Verify(s Signer, sig string, r io.Reader) error {
+	return s.verify(sig, r)
+}
+
+// VerifyBytes uses the Signer to verify that the signature is for the given
+// []bytes.
+//
+// Returns any errors from io.Reader, or ErrInvalidSig (use merry.Is(err,
+// mcrypto.ErrInvalidSig) to check).
+func VerifyBytes(s Signer, sig string, b []byte) error {
+	return s.verify(sig, bytes.NewBuffer(b))
+}
+
+// VerifyString uses the Signer to verify that the signature is for the given
+// string.
+//
+// Returns any errors from io.Reader, or ErrInvalidSig (use merry.Is(err,
+// mcrypto.ErrInvalidSig) to check).
+func VerifyString(s Signer, sig, in string) error {
+	return VerifyBytes(s, sig, []byte(in))
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+type signer struct {
+	outSize uint8 // in bytes, shouldn't be more than 32, cause sha256
+	secret  []byte
+}
+
+// NewSigner returns a Signer instance which will use the given secret to sign
+// and verify all signatures. The signatures generated by this Signer have no
+// expiration
+func NewSigner(secret []byte) Signer {
+	return signer{outSize: 20, secret: secret}
+}
+
+// NewWeakSigner returns a Signer, similar to how NewSigner does. The signatures
+// generated by this Signer will be smaller in text size, and therefore weaker,
+// but are still fine for most applications.
+//
+// The Signers returned by both NewSigner and NewWeakSigner can verify
+// each-other's signatures, as long as the secret is the same.
+func NewWeakSigner(secret []byte) Signer {
+	return signer{outSize: 8, secret: secret}
+}
+
+func (s signer) signRaw(r io.Reader) (hash.Hash, error) {
+	h := hmac.New(sha256.New, s.secret)
+	_, err := io.Copy(h, r)
+	return h, err
+}
+
+func (s signer) sign(r io.Reader) (string, error) {
+	h, err := s.signRaw(r)
+	if err != nil {
+		return "", err
+	}
+	b := make([]byte, 1+h.Size())
+	b[0] = s.outSize
+	h.Sum(b[1:1])
+	return sigV0 + hex.EncodeToString(b[:1+int(s.outSize)]), nil
+}
+
+func (s signer) verify(sig string, r io.Reader) error {
+	sig, ok := stripPrefix(sig, sigV0)
+	if !ok || len(sig) < 2 {
+		return mlog.ErrWithKV(errMalformedSig, mlog.KV{"sig": sig})
+	}
+	sig = strings.TrimPrefix(sig, sigV0)
+
+	sizeStr, sig := sig[:2], sig[2:]
+	sizeB, err := hex.DecodeString(sizeStr)
+	if err != nil {
+		return mlog.ErrWithKV(err, mlog.KV{"sig": sig})
+	}
+
+	size := sizeB[0]
+	if hex.DecodedLen(len(sig)) != int(size) {
+		return mlog.ErrWithKV(errMalformedSig, mlog.KV{"sig": sig})
+	}
+
+	sigB, err := hex.DecodeString(sig)
+	if err != nil {
+		return mlog.ErrWithKV(err, mlog.KV{"sig": sig})
+	}
+
+	h, err := s.signRaw(r)
+	if err != nil {
+		return mlog.ErrWithKV(err, mlog.KV{"sig": sig})
+	}
+
+	if !hmac.Equal(sigB, h.Sum(nil)[:size]) {
+		return mlog.ErrWithKV(ErrInvalidSig, mlog.KV{"sig": sig})
+	}
+
+	return nil
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+type expireSigner struct {
+	s       Signer
+	timeout time.Duration
+
+	// only used during tests
+	testNow time.Time
+}
+
+// ExpireSigner wraps a Signer so that the signatures produced include timestamp
+// information about when the signature was made. That information is then used
+// during verifying to ensure the signature isn't older than the timeout.
+//
+// It is allowed to change the timeout ExpireSigner is initialized with.
+// Previously generated signatures will be verified (or rejected) using the new
+// timeout.
+func ExpireSigner(s Signer, timeout time.Duration) Signer {
+	return expireSigner{s: s, timeout: timeout}
+}
+
+func (es expireSigner) now() time.Time {
+	if !es.testNow.IsZero() {
+		return es.testNow
+	}
+	return time.Now()
+}
+
+func (es expireSigner) sign(r io.Reader) (string, error) {
+	b := make([]byte, 8)
+	binary.BigEndian.PutUint64(b, uint64(es.now().UnixNano()))
+	sig, err := es.s.sign(prefixReader(r, b))
+	return exSigV0 + hex.EncodeToString(b) + sig, err
+}
+
+var exSigTimeLen = hex.EncodedLen(8)
+
+func (es expireSigner) verify(sig string, r io.Reader) error {
+	sig, ok := stripPrefix(sig, exSigV0)
+	if !ok || len(sig) < exSigTimeLen {
+		return mlog.ErrWithKV(errMalformedSig, mlog.KV{"sig": sig})
+	}
+
+	tStr, sig := sig[:exSigTimeLen], sig[exSigTimeLen:]
+	tB, err := hex.DecodeString(tStr)
+	if err != nil {
+		return mlog.ErrWithKV(err, mlog.KV{"sig": sig})
+	}
+
+	t := time.Unix(0, int64(binary.BigEndian.Uint64(tB)))
+	if es.now().Sub(t) > es.timeout {
+		return mlog.ErrWithKV(ErrInvalidSig, mlog.KV{"sig": sig})
+	}
+
+	return es.s.verify(sig, prefixReader(r, tB))
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+type uniqueSigner struct {
+	s        Signer
+	randSize uint8 // in bytes
+}
+
+// UniqueSigner wraps a Signer so that when data is signed some random data is
+// included in the signed data, and that random data is included in the
+// signature as well. This ensures that even for the same input data signatures
+// produced are all unique.
+func UniqueSigner(s Signer) Signer {
+	return uniqueSigner{s: s, randSize: 10}
+}
+
+func (us uniqueSigner) sign(r io.Reader) (string, error) {
+	b := make([]byte, 1+us.randSize)
+	b[0] = us.randSize
+	if _, err := rand.Read(b[1:]); err != nil {
+		panic(err)
+	}
+	sig, err := us.s.sign(prefixReader(r, b[1:]))
+	return uniqueSigV0 + hex.EncodeToString(b) + sig, err
+}
+
+func (us uniqueSigner) verify(sig string, r io.Reader) error {
+	sig, ok := stripPrefix(sig, uniqueSigV0)
+	if !ok || len(sig) < 2 {
+		return mlog.ErrWithKV(errMalformedSig, mlog.KV{"sig": sig})
+	}
+
+	sizeStr, sig := sig[:2], sig[2:]
+	sizeB, err := hex.DecodeString(sizeStr)
+	if err != nil {
+		return mlog.ErrWithKV(err, mlog.KV{"sig": sig})
+	}
+
+	size := sizeB[0]
+	sizeEnc := hex.EncodedLen(int(size))
+	if len(sig) < sizeEnc {
+		return mlog.ErrWithKV(errMalformedSig, mlog.KV{"sig": sig})
+	}
+
+	bStr, sig := sig[:sizeEnc], sig[sizeEnc:]
+	b, err := hex.DecodeString(bStr)
+	if err != nil {
+		return mlog.ErrWithKV(err, mlog.KV{"sig": sig})
+	}
+
+	return us.s.verify(sig, prefixReader(r, b))
+}
diff --git a/mcrypto/sig_test.go b/mcrypto/sig_test.go
new file mode 100644
index 0000000..50d5713
--- /dev/null
+++ b/mcrypto/sig_test.go
@@ -0,0 +1,80 @@
+package mcrypto
+
+import (
+	. "testing"
+	"time"
+
+	"github.com/ansel1/merry"
+	"github.com/mediocregopher/mediocre-go-lib/mtest"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestSigner(t *T) {
+	secret := mtest.RandBytes(16)
+	signer, weakSigner := NewSigner(secret), NewWeakSigner(secret)
+	var prevStr, prevSig, prevWeakSig string
+	for i := 0; i < 10000; i++ {
+		thisStr := mtest.RandHex(512)
+		thisSig := SignString(signer, thisStr)
+		thisWeakSig := SignString(weakSigner, thisStr)
+
+		// sanity checks
+		assert.NotEqual(t, thisSig, thisWeakSig)
+		assert.True(t, len(thisSig) > len(thisWeakSig))
+
+		// Either signer should be able to verify either signature
+		assert.NoError(t, VerifyString(signer, thisSig, thisStr))
+		assert.NoError(t, VerifyString(weakSigner, thisWeakSig, thisStr))
+		assert.NoError(t, VerifyString(signer, thisWeakSig, thisStr))
+		assert.NoError(t, VerifyString(weakSigner, thisSig, thisStr))
+
+		if prevStr != "" {
+			assert.NotEqual(t, prevSig, thisSig)
+			assert.NotEqual(t, prevWeakSig, thisWeakSig)
+			err := VerifyString(signer, prevSig, thisStr)
+			assert.True(t, merry.Is(err, ErrInvalidSig))
+			err = VerifyString(signer, prevWeakSig, thisStr)
+			assert.True(t, merry.Is(err, ErrInvalidSig))
+		}
+		prevStr = thisStr
+		prevSig = thisSig
+		prevWeakSig = thisWeakSig
+	}
+}
+
+func TestExpireSigner(t *T) {
+	origNow := time.Now()
+	s := ExpireSigner(NewSigner(mtest.RandBytes(16)), 1*time.Hour).(expireSigner)
+	s.testNow = origNow
+	str := mtest.RandHex(32)
+	sig := SignString(s, str)
+
+	// in the immediate the sig should obviously work
+	assert.NoError(t, VerifyString(s, sig, str))
+	err := VerifyString(s, sig, mtest.RandHex(32))
+	assert.True(t, merry.Is(err, ErrInvalidSig))
+
+	// within the timeout it should still work
+	s.testNow = s.testNow.Add(1 * time.Minute)
+	assert.NoError(t, VerifyString(s, sig, str))
+
+	// but a new "now" should then generate a different sig
+	sig2 := SignString(s, str)
+	assert.NotEqual(t, sig, sig2)
+	assert.NoError(t, VerifyString(s, sig2, str))
+
+	// jumping forward an hour should expire the first sig, but not the second
+	s.testNow = s.testNow.Add(1 * time.Hour)
+	err = VerifyString(s, sig, str)
+	assert.True(t, merry.Is(err, ErrInvalidSig))
+	assert.NoError(t, VerifyString(s, sig2, str))
+}
+
+func TestUniqueSigner(t *T) {
+	s := UniqueSigner(NewSigner(mtest.RandBytes(16)))
+	str := mtest.RandHex(32)
+	sigA, sigB := SignString(s, str), SignString(s, str)
+	assert.NotEqual(t, sigA, sigB)
+	assert.NoError(t, VerifyString(s, sigA, str))
+	assert.NoError(t, VerifyString(s, sigB, str))
+}
diff --git a/mcrypto/uuid.go b/mcrypto/uuid.go
index 58dd7a3..9308330 100644
--- a/mcrypto/uuid.go
+++ b/mcrypto/uuid.go
@@ -13,10 +13,7 @@ import (
 	"github.com/mediocregopher/mediocre-go-lib/mlog"
 )
 
-const (
-	uuidV0Prefix = "0u"
-	uuidV0Len    = 34 // prefix:2 + hexEncodedLen(time:8 + random:8)
-)
+var errMalformedUUID = errors.New("malformed UUID string")
 
 // UUID is a universally unique identifier which embeds within it a timestamp.
 //
@@ -43,7 +40,7 @@ func NewUUID(t time.Time) UUID {
 		panic(err)
 	}
 	return UUID{
-		str: uuidV0Prefix + hex.EncodeToString(b),
+		str: uuidV0 + hex.EncodeToString(b),
 	}
 }
 
@@ -80,7 +77,7 @@ func (u UUID) MarshalText() ([]byte, error) {
 // UnmarshalText implements the method for the encoding.TextUnmarshaler
 // interface
 func (u *UUID) UnmarshalText(b []byte) error {
-	if !bytes.HasPrefix(b, []byte(uuidV0Prefix)) || len(b) != uuidV0Len {
+	if !bytes.HasPrefix(b, []byte(uuidV0)) || len(b) != len(uuidV0)+32 {
 		err := errors.New("malformed uuid string")
 		return mlog.ErrWithKV(err, mlog.KV{"uuidStr": string(b)})
 	}
diff --git a/mcrypto/uuid_test.go b/mcrypto/uuid_test.go
index 00a0bbb..c0a3c9f 100644
--- a/mcrypto/uuid_test.go
+++ b/mcrypto/uuid_test.go
@@ -18,8 +18,7 @@ func TestUUID(t *T) {
 		this := NewUUID(thisT)
 
 		// basic
-		assert.True(t, strings.HasPrefix(this.String(), uuidV0Prefix))
-		assert.Len(t, this.String(), uuidV0Len)
+		assert.True(t, strings.HasPrefix(this.String(), uuidV0))
 
 		// comparisons with prev
 		assert.False(t, prev.Equal(this))
@@ -35,6 +34,6 @@ func TestUUID(t *T) {
 		require.NoError(t, err)
 		var this2 UUID
 		require.NoError(t, this2.UnmarshalText(thisStr))
-		assert.True(t, this.Equal(this2))
+		assert.True(t, this.Equal(this2), "this:%q this2:%q", this, this2)
 	}
 }