diff --git a/common/alloc/buffer.go b/common/alloc/buffer.go
index 8a0183e5..ed5c2131 100644
--- a/common/alloc/buffer.go
+++ b/common/alloc/buffer.go
@@ -108,6 +108,7 @@ func (b *Buffer) Bytes() []byte {
 }
 
 func (b *Buffer) SetBytesFunc(writer BytesWriter) {
+	b.start = defaultOffset
 	b.end = b.start + writer(b.v[b.start:])
 }
 
diff --git a/common/crypto/auth.go b/common/crypto/auth.go
index b73ebfe9..5f911d90 100644
--- a/common/crypto/auth.go
+++ b/common/crypto/auth.go
@@ -121,38 +121,38 @@ func (v *AuthenticationReader) CopyChunk(b []byte) int {
 	return nBytes
 }
 
+func (v *AuthenticationReader) EnsureChunk() error {
+	for {
+		err := v.NextChunk()
+		if err == nil {
+			return nil
+		}
+		if err == errInsufficientBuffer {
+			if !v.buffer.IsEmpty() {
+				leftover := v.buffer.Bytes()
+				v.buffer.SetBytesFunc(func(b []byte) int {
+					return copy(b, leftover)
+				})
+			}
+			_, err = v.buffer.FillFrom(v.reader)
+		}
+		return err
+	}
+}
+
 func (v *AuthenticationReader) Read(b []byte) (int, error) {
 	if len(v.chunk) > 0 {
 		nBytes := v.CopyChunk(b)
 		return nBytes, nil
 	}
 
-	totalBytes := 0
-	for {
-		err := v.NextChunk()
-		if err == errInsufficientBuffer {
-			if totalBytes > 0 {
-				return totalBytes, nil
-			}
-			leftover := v.buffer.Bytes()
-			v.buffer.SetBytesFunc(func(b []byte) int {
-				return copy(b, leftover)
-			})
-			_, err = v.buffer.FillFrom(v.reader)
-		}
-
-		if err != nil {
-			return 0, err
-		}
-
-		nBytes := v.CopyChunk(b)
-		b = b[nBytes:]
-		totalBytes += nBytes
-
-		if !v.aggressive {
-			return totalBytes, nil
-		}
+	err := v.EnsureChunk()
+	if err != nil {
+		return 0, err
 	}
+
+	nBytes := v.CopyChunk(b)
+	return nBytes, nil
 }
 
 type AuthenticationWriter struct {
diff --git a/common/io/reader_test.go b/common/io/reader_test.go
index ff6eb0c8..f57f48e9 100644
--- a/common/io/reader_test.go
+++ b/common/io/reader_test.go
@@ -25,5 +25,5 @@ func TestAdaptiveReader(t *testing.T) {
 	b2, err := reader.Read()
 	assert.Error(err).IsNil()
 	assert.Bool(b2.IsFull()).IsTrue()
-	assert.Int(buffer.Len()).Equals(778272)
+	assert.Int(buffer.Len()).Equals(1007648)
 }