mirror/openssl
2
0
Fork 0
mirror of https://github.com/openssl/openssl.git synced 2025-03-01 19:28:10 +08:00
Code Issues Packages Projects Releases Wiki Activity

Prevent over long nonces in ChaCha20-Poly1305

Browse Source 
ChaCha20-Poly1305 is an AEAD cipher, and requires a unique nonce input for
every encryption operation. RFC 7539 specifies that the nonce value (IV)
should be 96 bits (12 bytes). OpenSSL allows a variable nonce length and
front pads the nonce with 0 bytes if it is less than 12 bytes. However it
also incorrectly allows a nonce to be set of up to 16 bytes. In this case
only the last 12 bytes are significant and any additional leading bytes are
ignored.

It is a requirement of using this cipher that nonce values are unique.
Messages encrypted using a reused nonce value are susceptible to serious
confidentiality and integrity attacks. If an application changes the
default nonce length to be longer than 12 bytes and then makes a change to
the leading bytes of the nonce expecting the new value to be a new unique
nonce then such an application could inadvertently encrypt messages with a
reused nonce.

Additionally the ignored bytes in a long nonce are not covered by the
integrity guarantee of this cipher. Any application that relies on the
integrity of these ignored leading bytes of a long nonce may be further
affected.

Any OpenSSL internal use of this cipher, including in SSL/TLS, is safe
because no such use sets such a long nonce value. However user
applications that use this cipher directly and set a non-default nonce
length to be longer than 12 bytes may be vulnerable.

CVE-2019-1543

Fixes #8345

Reviewed-by: Paul Dale <paul.dale@oracle.com>
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/8406)
This commit is contained in:
Matt Caswell 2019-03-05 14:39:15 +00:00
parent 18e1e30245
commit 2a3d0ee9d5
1 changed files with 3 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
crypto/evp/e_chacha20_poly1305.c
View File

@ -30,6 +30,8 @@ typedef struct {
#define data(ctx) ((EVP_CHACHA_KEY *)(ctx)->cipher_data)
#define CHACHA20_POLY1305_MAX_IVLEN 12
static int chacha_init_key(EVP_CIPHER_CTX *ctx,
const unsigned char user_key[CHACHA_KEY_SIZE],
const unsigned char iv[CHACHA_CTR_SIZE], int enc)
@ -533,7 +535,7 @@ static int chacha20_poly1305_ctrl(EVP_CIPHER_CTX *ctx, int type, int arg,
return 1;
case EVP_CTRL_AEAD_SET_IVLEN:
if (arg <= 0 || arg > CHACHA_CTR_SIZE)
if (arg <= 0 || arg > CHACHA20_POLY1305_MAX_IVLEN)
return 0;
actx->nonce_len = arg;
return 1;