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internal/crypto: small simplifications

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* append operates on len, not cap (not a bug since len is set to cap above, but let's avoid the confusion)
* no need to extend ciphertext again to cap after we made it big enough
* make consistent use of ciphertext[:ivSize] vs iv[:]
* make all input problems errors and impossible/catastrophic cases panics
This commit is contained in:
Filippo Valsorda 2017-08-28 19:18:29 +02:00 committed by Filippo Valsorda
parent 3559f9c776
commit 9940e8d9f1
1 changed files with 13 additions and 18 deletions
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31
internal/crypto/crypto.go
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@ -251,21 +251,19 @@ func (k *Key) Encrypt(ciphertext []byte, plaintext []byte) ([]byte, error) {
// extend ciphertext slice if necessary // extend ciphertext slice if necessary
if len(ciphertext) < len(plaintext)+Extension { if len(ciphertext) < len(plaintext)+Extension {
ext := len(plaintext) + Extension - cap(ciphertext) ext := len(plaintext) + Extension - len(ciphertext)
ciphertext = append(ciphertext, make([]byte, ext)...) ciphertext = append(ciphertext, make([]byte, ext)...)
ciphertext = ciphertext[:cap(ciphertext)]
} }
iv := newIV() iv := newIV()
copy(ciphertext, iv[:])
c, err := aes.NewCipher(k.EncryptionKey[:]) c, err := aes.NewCipher(k.EncryptionKey[:])
if err != nil { if err != nil {
panic(fmt.Sprintf("unable to create cipher: %v", err)) panic(fmt.Sprintf("unable to create cipher: %v", err))
} }
e := cipher.NewCTR(c, ciphertext[:ivSize])
e := cipher.NewCTR(c, iv[:])
e.XORKeyStream(ciphertext[ivSize:], plaintext) e.XORKeyStream(ciphertext[ivSize:], plaintext)
copy(ciphertext, iv[:])
// truncate to only cover iv and actual ciphertext // truncate to only cover iv and actual ciphertext
ciphertext = ciphertext[:ivSize+len(plaintext)] ciphertext = ciphertext[:ivSize+len(plaintext)]
@ -285,12 +283,12 @@ func (k *Key) Decrypt(plaintext []byte, ciphertextWithMac []byte) (int, error) {
} }
// check for plausible length // check for plausible length
if len(ciphertextWithMac) < ivSize+macSize { if len(ciphertextWithMac) < Extension {
panic("trying to decrypt invalid data: ciphertext too small") return 0, errors.Errorf("trying to decrypt invalid data: ciphertext too small")
} }
// check buffer length for plaintext // check buffer length for plaintext
plaintextLength := len(ciphertextWithMac) - ivSize - macSize plaintextLength := len(ciphertextWithMac) - Extension
if len(plaintext) < plaintextLength { if len(plaintext) < plaintextLength {
return 0, errors.Errorf("plaintext buffer too small, %d < %d", len(plaintext), plaintextLength) return 0, errors.Errorf("plaintext buffer too small, %d < %d", len(plaintext), plaintextLength)
} }
@ -299,16 +297,16 @@ func (k *Key) Decrypt(plaintext []byte, ciphertextWithMac []byte) (int, error) {
l := len(ciphertextWithMac) - macSize l := len(ciphertextWithMac) - macSize
ciphertextWithIV, mac := ciphertextWithMac[:l], ciphertextWithMac[l:] ciphertextWithIV, mac := ciphertextWithMac[:l], ciphertextWithMac[l:]
// verify mac
if !poly1305Verify(ciphertextWithIV[ivSize:], ciphertextWithIV[:ivSize], &k.MACKey, mac) {
return 0, ErrUnauthenticated
}
// extract iv // extract iv
iv, ciphertext := ciphertextWithIV[:ivSize], ciphertextWithIV[ivSize:] iv, ciphertext := ciphertextWithIV[:ivSize], ciphertextWithIV[ivSize:]
// verify mac
if !poly1305Verify(ciphertext, iv, &k.MACKey, mac) {
return 0, ErrUnauthenticated
}
if len(ciphertext) != plaintextLength { if len(ciphertext) != plaintextLength {
return 0, errors.Errorf("plaintext and ciphertext lengths do not match: %d != %d", len(ciphertext), plaintextLength) panic("plaintext and ciphertext lengths do not match")
} }
// decrypt data // decrypt data
@ -316,10 +314,7 @@ func (k *Key) Decrypt(plaintext []byte, ciphertextWithMac []byte) (int, error) {
if err != nil { if err != nil {
panic(fmt.Sprintf("unable to create cipher: %v", err)) panic(fmt.Sprintf("unable to create cipher: %v", err))
} }
// decrypt
e := cipher.NewCTR(c, iv) e := cipher.NewCTR(c, iv)
plaintext = plaintext[:len(ciphertext)]
e.XORKeyStream(plaintext, ciphertext) e.XORKeyStream(plaintext, ciphertext)
return plaintextLength, nil return plaintextLength, nil