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Update decryp function

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* Do not use AAD
* Do not try to decrypt the last 16 bytes as Android adds the tag there
by default

Signed-off-by: Roeland Jago Douma <roeland@famdouma.nl>
This commit is contained in:
Roeland Jago Douma 2017-10-24 15:48:44 +02:00
parent bacbf337d2
commit ca6fa7b341
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GPG key ID: F941078878347C0C
1 changed files with 6 additions and 13 deletions
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19
src/libsync/clientsideencryption.cpp
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@ -119,8 +119,6 @@ namespace {
int decrypt(unsigned char *ciphertext,
int ciphertext_len,
unsigned char *aad,
int aad_len,
unsigned char *tag,
unsigned char *key,
unsigned char *iv,
@ -143,7 +141,7 @@ namespace {
handleErrors();
}
/* Set IV length. Not necessary if this is 12 bytes (96 bits) */
/* Set IV length to 16 bytes */
if(!EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, 16, NULL)) {
qCInfo(lcCse()) << "Error seting th iv length for the decrypt context";
handleErrors();
@ -155,18 +153,13 @@ namespace {
handleErrors();
}
/* Provide any AAD data. This can be called zero or more times as
* required
*/
if(!EVP_DecryptUpdate(ctx, NULL, &len, aad, aad_len)) {
qCInfo(lcCse()) << "Error updating the decrypt context with aad information";
handleErrors();
}
/* Provide the message to be decrypted, and obtain the plaintext output.
/* Provide the message to be decrypted, and obtain the plaintext output.
* EVP_DecryptUpdate can be called multiple times if necessary
*
* Do not try to decrypt the last 16 bytes. The tag is appended by Android.
* So we ignore the last 16 bytes.
*/
if(!EVP_DecryptUpdate(ctx, plaintext, &len, ciphertext, ciphertext_len)) {
if(!EVP_DecryptUpdate(ctx, plaintext, &len, ciphertext, ciphertext_len - 16)) {
qCInfo(lcCse()) << "Error decrypting the text";
handleErrors();
}