From 2a3d0ee9d59156c48973592331404471aca886d6 Mon Sep 17 00:00:00 2001 From: Matt Caswell Date: Tue, 5 Mar 2019 14:39:15 +0000 Subject: [PATCH] Prevent over long nonces in ChaCha20-Poly1305 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 Reviewed-by: Richard Levitte (Merged from https://github.com/openssl/openssl/pull/8406) --- crypto/evp/e_chacha20_poly1305.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/crypto/evp/e_chacha20_poly1305.c b/crypto/evp/e_chacha20_poly1305.c index e8a323f3be..37902000a0 100644 --- a/crypto/evp/e_chacha20_poly1305.c +++ b/crypto/evp/e_chacha20_poly1305.c @@ -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; -- 2.25.1