Slightly refactored error messages

[gogost.git] / mgm / mode.go

diff --git a/mgm/mode.go b/mgm/mode.go
index 3fdeaba0fbc889ca6baa59c645751bcec9d7e7d4..50abfd46afd78a21bf087a786e2b71cee5e1118a 100644 (file)
--- a/mgm/mode.go
+++ b/mgm/mode.go
@@ -21,6 +21,7 @@ import (
        "crypto/hmac"
        "encoding/binary"
        "errors"
+       "fmt"
 )
 
 var InvalidTag = errors.New("gogost/mgm: invalid authentication tag")
@@ -45,10 +46,10 @@ type MGM struct {
 func NewMGM(cipher cipher.Block, tagSize int) (cipher.AEAD, error) {
        blockSize := cipher.BlockSize()
        if !(blockSize == 8 || blockSize == 16) {
-               return nil, errors.New("gogost/mgm: only 64/128 blocksizes allowed")
+               return nil, errors.New("gogost/mgm: only {64|128} blocksizes allowed")
        }
        if tagSize < 4 || tagSize > blockSize {
-               return nil, errors.New("gogost/mgm: invalid tag size")
+               return nil, fmt.Errorf("gogost/mgm: invalid tag size (4<=%d<=%d)", tagSize, blockSize)
        }
        mgm := MGM{
                MaxSize:   uint64(1<<uint(blockSize*8/2) - 1),
@@ -215,7 +216,7 @@ func (mgm *MGM) Open(dst, nonce, ciphertext, additionalData []byte) ([]byte, err
        mgm.validateNonce(nonce)
        mgm.validateSizes(ciphertext, additionalData)
        if len(ciphertext) < mgm.TagSize {
-               return nil, errors.New("ciphertext is too short")
+               return nil, fmt.Errorf("ciphertext is too short (%d<%d)", len(ciphertext), mgm.TagSize)
        }
        if uint64(len(ciphertext)-mgm.TagSize) > mgm.MaxSize {
                panic("ciphertext is too big")