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crypto: ecdh - explicitly zeroize private_key

PATCH In review Joachim Vandersmissen 2 participants 2 messages Mar 28, 2024 – Apr 5, 2024 Crypto API

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Joachim Vandersmissen

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PATCH v2 1/1 crypto: ecdh - explicitly zeroize private_key

private_key is overwritten with the key parameter passed in by the caller (if present), or alternatively a newly generated private key. However, it is possible that the caller provides a key (or the newly generated key) which is shorter than the previous key. In that scenario, some key material from the previous key would not be overwritten. The easiest solution is to explicitly zeroize the entire private_key array first.

Note that this patch slightly changes the behavior of this function:
previously, if the ecc_gen_privkey failed, the old private_key would remain. Now, the private_key is always zeroized. This behavior is consistent with the case where params.key is set and ecc_is_key_valid fails.

Signed-off-by Joachim Vandersmissen <[email protected]>
---
 crypto/ecdh.c | 2 ++
 1 file changed, 2 insertions(+)
crypto/ecdh.c +2 -0
index 80afee3234fb..3049f147e011 100644
@@ -33,6 +33,8 @@ static int ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
 	    params.key_size > sizeof(u64) * ctx->ndigits)
 		return -EINVAL;
 
+	memset(ctx->private_key, 0, sizeof(ctx->private_key));
+
 	if (!params.key || !params.key_size)
 		return ecc_gen_privkey(ctx->curve_id, ctx->ndigits,
 				       ctx->private_key);
Signature · 1 line
2.44.0
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#1 lore raw
Quoted 14 lines · Joachim Vandersmissen

private_key is overwritten with the key parameter passed in by the caller (if present), or alternatively a newly generated private key. However, it is possible that the caller provides a key (or the newly generated key) which is shorter than the previous key. In that scenario, some key material from the previous key would not be overwritten. The easiest solution is to explicitly zeroize the entire private_key array first.

Note that this patch slightly changes the behavior of this function:
previously, if the ecc_gen_privkey failed, the old private_key would remain. Now, the private_key is always zeroized. This behavior is consistent with the case where params.key is set and ecc_is_key_valid fails.

Quoted 4 lines
Signed-off-by Joachim Vandersmissen <[email protected]>
---
 crypto/ecdh.c | 2 ++
 1 file changed, 2 insertions(+)

Patch applied. Thanks.

Signature · 3 lines
Email: Herbert Xu <[email protected]>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt