[PATCH v2 0/2] crypto: ecdh & ecc: Fix private key byte ordering issues

[PATCH v2 0/2] crypto: ecdh & ecc: Fix private key byte ordering issues

[Stefan Berger]

The 1st patch fixes a byte ordering issue where ctx->private_key is
currently passed to ecc_is_key_valid but the key is in reverse byte order.
To solve this issue it introduces the variable 'priv' that is already used
throughout the ecc and ecdh code bases for a private key in proper byte
order and calls the function with 'priv'.

The 2nd patch gets rid of the 'priv' variable wherever it is used to hold
a private key (byte-swapped initialized from ctx->private_key) in proper
byte order and uses ctx->private_key directly that is now initialized in
proper byte order.

Regards,
  Stefan

v2:
  - Added missing zeroizing of priv variable (1/2)
  - Improved patch description (2/2)


Stefan Berger (2):
  crypto: ecdh - Pass private key in proper byte order to check valid
    key
  crypto: ecdh & ecc - Initialize ctx->private_key in proper byte order

 crypto/ecc.c                  | 29 ++++++++++-------------------
 crypto/ecdh.c                 |  9 ++++++---
 include/crypto/internal/ecc.h |  3 ++-
 3 files changed, 18 insertions(+), 23 deletions(-)

-- 
2.43.0

[PATCH v2 1/2] crypto: ecdh - Pass private key in proper byte order to check valid key

[Stefan Berger]

ecc_is_key_valid expects a key with the most significant digit in the last
entry of the digit array. Currently ecdh_set_secret passes a reversed key
to ecc_is_key_valid that then passes the rather simple test checking
whether the private key is in range [2, n-3]. For all current ecdh-
supported curves (NIST P192/256/384) the 'n' parameter is a rather large
number, therefore easily passing this test.

Throughout the ecdh and ecc codebase the variable 'priv' is used for a
private_key holding the bytes in proper byte order. Therefore, introduce
priv in ecdh_set_secret and copy the bytes from ctx->private_key into
priv in proper byte order by using ecc_swap_digits. Pass priv to
ecc_is_valid_key.

Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Salvatore Benedetto <salvatore.benedetto@intel.com>
Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
---
 crypto/ecdh.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/crypto/ecdh.c b/crypto/ecdh.c
index 3049f147e011..c02c9a2b9682 100644
--- a/crypto/ecdh.c
+++ b/crypto/ecdh.c
@@ -27,7 +27,9 @@ static int ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
 			   unsigned int len)
 {
 	struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
+	u64 priv[ECC_MAX_DIGITS];
 	struct ecdh params;
+	int ret = 0;
 
 	if (crypto_ecdh_decode_key(buf, len, &params) < 0 ||
 	    params.key_size > sizeof(u64) * ctx->ndigits)
@@ -40,13 +42,16 @@ static int ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
 				       ctx->private_key);
 
 	memcpy(ctx->private_key, params.key, params.key_size);
+	ecc_swap_digits(ctx->private_key, priv, ctx->ndigits);
 
 	if (ecc_is_key_valid(ctx->curve_id, ctx->ndigits,
-			     ctx->private_key, params.key_size) < 0) {
+			     priv, params.key_size) < 0) {
 		memzero_explicit(ctx->private_key, params.key_size);
-		return -EINVAL;
+		ret = -EINVAL;
 	}
-	return 0;
+	memzero_explicit(priv, sizeof(priv));
+
+	return ret;
 }
 
 static int ecdh_compute_value(struct kpp_request *req)
-- 
2.43.0

Re: [PATCH v2 1/2] crypto: ecdh - Pass private key in proper byte order to check valid key

[Jarkko Sakkinen]

On Wed Apr 17, 2024 at 7:21 PM EEST, Stefan Berger wrote:
> ecc_is_key_valid expects a key with the most significant digit in the last
> entry of the digit array. Currently ecdh_set_secret passes a reversed key
> to ecc_is_key_valid that then passes the rather simple test checking
> whether the private key is in range [2, n-3]. For all current ecdh-
> supported curves (NIST P192/256/384) the 'n' parameter is a rather large
> number, therefore easily passing this test.
>
> Throughout the ecdh and ecc codebase the variable 'priv' is used for a
> private_key holding the bytes in proper byte order. Therefore, introduce
> priv in ecdh_set_secret and copy the bytes from ctx->private_key into
> priv in proper byte order by using ecc_swap_digits. Pass priv to
> ecc_is_valid_key.
>
> Cc: Ard Biesheuvel <ardb@kernel.org>
> Cc: Salvatore Benedetto <salvatore.benedetto@intel.com>
> Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
> ---
>  crypto/ecdh.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/crypto/ecdh.c b/crypto/ecdh.c
> index 3049f147e011..c02c9a2b9682 100644
> --- a/crypto/ecdh.c
> +++ b/crypto/ecdh.c
> @@ -27,7 +27,9 @@ static int ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
>  			   unsigned int len)
>  {
>  	struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
> +	u64 priv[ECC_MAX_DIGITS];
>  	struct ecdh params;
> +	int ret = 0;
>  
>  	if (crypto_ecdh_decode_key(buf, len, &params) < 0 ||
>  	    params.key_size > sizeof(u64) * ctx->ndigits)
> @@ -40,13 +42,16 @@ static int ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
>  				       ctx->private_key);
>  
>  	memcpy(ctx->private_key, params.key, params.key_size);
> +	ecc_swap_digits(ctx->private_key, priv, ctx->ndigits);
>  
>  	if (ecc_is_key_valid(ctx->curve_id, ctx->ndigits,
> -			     ctx->private_key, params.key_size) < 0) {
> +			     priv, params.key_size) < 0) {
>  		memzero_explicit(ctx->private_key, params.key_size);
> -		return -EINVAL;
> +		ret = -EINVAL;
>  	}
> -	return 0;
> +	memzero_explicit(priv, sizeof(priv));
> +
> +	return ret;
>  }
>  
>  static int ecdh_compute_value(struct kpp_request *req)

Acked-by: Jarkko Sakkinen <jarkko@kernel.org>

BR, Jarkko

[PATCH v2 2/2] crypto: ecdh & ecc - Initialize ctx->private_key in proper byte order

[Stefan Berger]

The private key in ctx->private_key is currently initialized in reverse
byte order in ecdh_set_secret and whenever the key is needed in proper
byte order the variable priv is introduced and the bytes from
ctx->private_key are copied into priv while being byte-swapped
(ecc_swap_digits). To get rid of the unnecessary byte swapping initialize
ctx->private_key in proper byte order and clean up all functions that were
previously using priv or were called with ctx->private_key:

- ecc_gen_privkey: Directly initialize the passed ctx->private_key with
  random bytes and get rid of the priv variable. This function only has
  ecdh_set_secret as a caller.

- crypto_ecdh_shared_secret: Called only from ecdh_compute_value with
  ctx->private_key. Get rid of the priv variable and work with the passed
  private_key directly.

- ecc_make_pub_key: Called only from ecdh_compute_value with
  ctx->private_key. Get rid of the priv variable and work with the passed
  private_key directly.

Cc: Salvatore Benedetto <salvatore.benedetto@intel.com>
Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
---
 crypto/ecc.c                  | 29 ++++++++++-------------------
 crypto/ecdh.c                 |  8 +++-----
 include/crypto/internal/ecc.h |  3 ++-
 3 files changed, 15 insertions(+), 25 deletions(-)

diff --git a/crypto/ecc.c b/crypto/ecc.c
index 2e05387b9499..c1d2e884be1e 100644
--- a/crypto/ecc.c
+++ b/crypto/ecc.c
@@ -1497,10 +1497,10 @@ EXPORT_SYMBOL(ecc_is_key_valid);
  * This method generates a private key uniformly distributed in the range
  * [2, n-3].
  */
-int ecc_gen_privkey(unsigned int curve_id, unsigned int ndigits, u64 *privkey)
+int ecc_gen_privkey(unsigned int curve_id, unsigned int ndigits,
+		    u64 *private_key)
 {
 	const struct ecc_curve *curve = ecc_get_curve(curve_id);
-	u64 priv[ECC_MAX_DIGITS];
 	unsigned int nbytes = ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
 	unsigned int nbits = vli_num_bits(curve->n, ndigits);
 	int err;
@@ -1509,7 +1509,7 @@ int ecc_gen_privkey(unsigned int curve_id, unsigned int ndigits, u64 *privkey)
 	 * Step 1 & 2: check that N is included in Table 1 of FIPS 186-5,
 	 * section 6.1.1.
 	 */
-	if (nbits < 224 || ndigits > ARRAY_SIZE(priv))
+	if (nbits < 224)
 		return -EINVAL;
 
 	/*
@@ -1527,17 +1527,16 @@ int ecc_gen_privkey(unsigned int curve_id, unsigned int ndigits, u64 *privkey)
 		return -EFAULT;
 
 	/* Step 3: obtain N returned_bits from the DRBG. */
-	err = crypto_rng_get_bytes(crypto_default_rng, (u8 *)priv, nbytes);
+	err = crypto_rng_get_bytes(crypto_default_rng,
+				   (u8 *)private_key, nbytes);
 	crypto_put_default_rng();
 	if (err)
 		return err;
 
 	/* Step 4: make sure the private key is in the valid range. */
-	if (__ecc_is_key_valid(curve, priv, ndigits))
+	if (__ecc_is_key_valid(curve, private_key, ndigits))
 		return -EINVAL;
 
-	ecc_swap_digits(priv, privkey, ndigits);
-
 	return 0;
 }
 EXPORT_SYMBOL(ecc_gen_privkey);
@@ -1547,23 +1546,20 @@ int ecc_make_pub_key(unsigned int curve_id, unsigned int ndigits,
 {
 	int ret = 0;
 	struct ecc_point *pk;
-	u64 priv[ECC_MAX_DIGITS];
 	const struct ecc_curve *curve = ecc_get_curve(curve_id);
 
-	if (!private_key || ndigits > ARRAY_SIZE(priv)) {
+	if (!private_key) {
 		ret = -EINVAL;
 		goto out;
 	}
 
-	ecc_swap_digits(private_key, priv, ndigits);
-
 	pk = ecc_alloc_point(ndigits);
 	if (!pk) {
 		ret = -ENOMEM;
 		goto out;
 	}
 
-	ecc_point_mult(pk, &curve->g, priv, NULL, curve, ndigits);
+	ecc_point_mult(pk, &curve->g, private_key, NULL, curve, ndigits);
 
 	/* SP800-56A rev 3 5.6.2.1.3 key check */
 	if (ecc_is_pubkey_valid_full(curve, pk)) {
@@ -1647,13 +1643,11 @@ int crypto_ecdh_shared_secret(unsigned int curve_id, unsigned int ndigits,
 {
 	int ret = 0;
 	struct ecc_point *product, *pk;
-	u64 priv[ECC_MAX_DIGITS];
 	u64 rand_z[ECC_MAX_DIGITS];
 	unsigned int nbytes;
 	const struct ecc_curve *curve = ecc_get_curve(curve_id);
 
-	if (!private_key || !public_key ||
-	    ndigits > ARRAY_SIZE(priv) || ndigits > ARRAY_SIZE(rand_z)) {
+	if (!private_key || !public_key || ndigits > ARRAY_SIZE(rand_z)) {
 		ret = -EINVAL;
 		goto out;
 	}
@@ -1674,15 +1668,13 @@ int crypto_ecdh_shared_secret(unsigned int curve_id, unsigned int ndigits,
 	if (ret)
 		goto err_alloc_product;
 
-	ecc_swap_digits(private_key, priv, ndigits);
-
 	product = ecc_alloc_point(ndigits);
 	if (!product) {
 		ret = -ENOMEM;
 		goto err_alloc_product;
 	}
 
-	ecc_point_mult(product, pk, priv, rand_z, curve, ndigits);
+	ecc_point_mult(product, pk, private_key, rand_z, curve, ndigits);
 
 	if (ecc_point_is_zero(product)) {
 		ret = -EFAULT;
@@ -1692,7 +1684,6 @@ int crypto_ecdh_shared_secret(unsigned int curve_id, unsigned int ndigits,
 	ecc_swap_digits(product->x, secret, ndigits);
 
 err_validity:
-	memzero_explicit(priv, sizeof(priv));
 	memzero_explicit(rand_z, sizeof(rand_z));
 	ecc_free_point(product);
 err_alloc_product:
diff --git a/crypto/ecdh.c b/crypto/ecdh.c
index c02c9a2b9682..72cfd1590156 100644
--- a/crypto/ecdh.c
+++ b/crypto/ecdh.c
@@ -27,7 +27,6 @@ static int ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
 			   unsigned int len)
 {
 	struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
-	u64 priv[ECC_MAX_DIGITS];
 	struct ecdh params;
 	int ret = 0;
 
@@ -41,15 +40,14 @@ static int ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
 		return ecc_gen_privkey(ctx->curve_id, ctx->ndigits,
 				       ctx->private_key);
 
-	memcpy(ctx->private_key, params.key, params.key_size);
-	ecc_swap_digits(ctx->private_key, priv, ctx->ndigits);
+	ecc_digits_from_bytes(params.key, params.key_size,
+			      ctx->private_key, ctx->ndigits);
 
 	if (ecc_is_key_valid(ctx->curve_id, ctx->ndigits,
-			     priv, params.key_size) < 0) {
+			     ctx->private_key, params.key_size) < 0) {
 		memzero_explicit(ctx->private_key, params.key_size);
 		ret = -EINVAL;
 	}
-	memzero_explicit(priv, sizeof(priv));
 
 	return ret;
 }
diff --git a/include/crypto/internal/ecc.h b/include/crypto/internal/ecc.h
index 4e2f5f938e91..7ca1f463d1ec 100644
--- a/include/crypto/internal/ecc.h
+++ b/include/crypto/internal/ecc.h
@@ -103,7 +103,8 @@ int ecc_is_key_valid(unsigned int curve_id, unsigned int ndigits,
  * Returns 0 if the private key was generated successfully, a negative value
  * if an error occurred.
  */
-int ecc_gen_privkey(unsigned int curve_id, unsigned int ndigits, u64 *privkey);
+int ecc_gen_privkey(unsigned int curve_id, unsigned int ndigits,
+		    u64 *private_key);
 
 /**
  * ecc_make_pub_key() - Compute an ECC public key
-- 
2.43.0

Re: [PATCH v2 2/2] crypto: ecdh & ecc - Initialize ctx->private_key in proper byte order

[Jarkko Sakkinen]

On Wed Apr 17, 2024 at 7:21 PM EEST, Stefan Berger wrote:
> The private key in ctx->private_key is currently initialized in reverse
> byte order in ecdh_set_secret and whenever the key is needed in proper
> byte order the variable priv is introduced and the bytes from
> ctx->private_key are copied into priv while being byte-swapped
> (ecc_swap_digits). To get rid of the unnecessary byte swapping initialize
> ctx->private_key in proper byte order and clean up all functions that were
> previously using priv or were called with ctx->private_key:
>
> - ecc_gen_privkey: Directly initialize the passed ctx->private_key with
>   random bytes and get rid of the priv variable. This function only has
>   ecdh_set_secret as a caller.
>
> - crypto_ecdh_shared_secret: Called only from ecdh_compute_value with
>   ctx->private_key. Get rid of the priv variable and work with the passed
>   private_key directly.
>
> - ecc_make_pub_key: Called only from ecdh_compute_value with
>   ctx->private_key. Get rid of the priv variable and work with the passed
>   private_key directly.
>
> Cc: Salvatore Benedetto <salvatore.benedetto@intel.com>
> Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
> ---
>  crypto/ecc.c                  | 29 ++++++++++-------------------
>  crypto/ecdh.c                 |  8 +++-----
>  include/crypto/internal/ecc.h |  3 ++-
>  3 files changed, 15 insertions(+), 25 deletions(-)
>
> diff --git a/crypto/ecc.c b/crypto/ecc.c
> index 2e05387b9499..c1d2e884be1e 100644
> --- a/crypto/ecc.c
> +++ b/crypto/ecc.c
> @@ -1497,10 +1497,10 @@ EXPORT_SYMBOL(ecc_is_key_valid);
>   * This method generates a private key uniformly distributed in the range
>   * [2, n-3].
>   */
> -int ecc_gen_privkey(unsigned int curve_id, unsigned int ndigits, u64 *privkey)
> +int ecc_gen_privkey(unsigned int curve_id, unsigned int ndigits,
> +		    u64 *private_key)
>  {
>  	const struct ecc_curve *curve = ecc_get_curve(curve_id);
> -	u64 priv[ECC_MAX_DIGITS];
>  	unsigned int nbytes = ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
>  	unsigned int nbits = vli_num_bits(curve->n, ndigits);
>  	int err;
> @@ -1509,7 +1509,7 @@ int ecc_gen_privkey(unsigned int curve_id, unsigned int ndigits, u64 *privkey)
>  	 * Step 1 & 2: check that N is included in Table 1 of FIPS 186-5,
>  	 * section 6.1.1.
>  	 */
> -	if (nbits < 224 || ndigits > ARRAY_SIZE(priv))
> +	if (nbits < 224)
>  		return -EINVAL;
>  
>  	/*
> @@ -1527,17 +1527,16 @@ int ecc_gen_privkey(unsigned int curve_id, unsigned int ndigits, u64 *privkey)
>  		return -EFAULT;
>  
>  	/* Step 3: obtain N returned_bits from the DRBG. */
> -	err = crypto_rng_get_bytes(crypto_default_rng, (u8 *)priv, nbytes);
> +	err = crypto_rng_get_bytes(crypto_default_rng,
> +				   (u8 *)private_key, nbytes);
>  	crypto_put_default_rng();
>  	if (err)
>  		return err;
>  
>  	/* Step 4: make sure the private key is in the valid range. */
> -	if (__ecc_is_key_valid(curve, priv, ndigits))
> +	if (__ecc_is_key_valid(curve, private_key, ndigits))
>  		return -EINVAL;
>  
> -	ecc_swap_digits(priv, privkey, ndigits);
> -
>  	return 0;
>  }
>  EXPORT_SYMBOL(ecc_gen_privkey);
> @@ -1547,23 +1546,20 @@ int ecc_make_pub_key(unsigned int curve_id, unsigned int ndigits,
>  {
>  	int ret = 0;
>  	struct ecc_point *pk;
> -	u64 priv[ECC_MAX_DIGITS];
>  	const struct ecc_curve *curve = ecc_get_curve(curve_id);
>  
> -	if (!private_key || ndigits > ARRAY_SIZE(priv)) {
> +	if (!private_key) {
>  		ret = -EINVAL;
>  		goto out;
>  	}
>  
> -	ecc_swap_digits(private_key, priv, ndigits);
> -
>  	pk = ecc_alloc_point(ndigits);
>  	if (!pk) {
>  		ret = -ENOMEM;
>  		goto out;
>  	}
>  
> -	ecc_point_mult(pk, &curve->g, priv, NULL, curve, ndigits);
> +	ecc_point_mult(pk, &curve->g, private_key, NULL, curve, ndigits);
>  
>  	/* SP800-56A rev 3 5.6.2.1.3 key check */
>  	if (ecc_is_pubkey_valid_full(curve, pk)) {
> @@ -1647,13 +1643,11 @@ int crypto_ecdh_shared_secret(unsigned int curve_id, unsigned int ndigits,
>  {
>  	int ret = 0;
>  	struct ecc_point *product, *pk;
> -	u64 priv[ECC_MAX_DIGITS];
>  	u64 rand_z[ECC_MAX_DIGITS];
>  	unsigned int nbytes;
>  	const struct ecc_curve *curve = ecc_get_curve(curve_id);
>  
> -	if (!private_key || !public_key ||
> -	    ndigits > ARRAY_SIZE(priv) || ndigits > ARRAY_SIZE(rand_z)) {
> +	if (!private_key || !public_key || ndigits > ARRAY_SIZE(rand_z)) {
>  		ret = -EINVAL;
>  		goto out;
>  	}
> @@ -1674,15 +1668,13 @@ int crypto_ecdh_shared_secret(unsigned int curve_id, unsigned int ndigits,
>  	if (ret)
>  		goto err_alloc_product;
>  
> -	ecc_swap_digits(private_key, priv, ndigits);
> -
>  	product = ecc_alloc_point(ndigits);
>  	if (!product) {
>  		ret = -ENOMEM;
>  		goto err_alloc_product;
>  	}
>  
> -	ecc_point_mult(product, pk, priv, rand_z, curve, ndigits);
> +	ecc_point_mult(product, pk, private_key, rand_z, curve, ndigits);
>  
>  	if (ecc_point_is_zero(product)) {
>  		ret = -EFAULT;
> @@ -1692,7 +1684,6 @@ int crypto_ecdh_shared_secret(unsigned int curve_id, unsigned int ndigits,
>  	ecc_swap_digits(product->x, secret, ndigits);
>  
>  err_validity:
> -	memzero_explicit(priv, sizeof(priv));
>  	memzero_explicit(rand_z, sizeof(rand_z));
>  	ecc_free_point(product);
>  err_alloc_product:
> diff --git a/crypto/ecdh.c b/crypto/ecdh.c
> index c02c9a2b9682..72cfd1590156 100644
> --- a/crypto/ecdh.c
> +++ b/crypto/ecdh.c
> @@ -27,7 +27,6 @@ static int ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
>  			   unsigned int len)
>  {
>  	struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
> -	u64 priv[ECC_MAX_DIGITS];
>  	struct ecdh params;
>  	int ret = 0;
>  
> @@ -41,15 +40,14 @@ static int ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
>  		return ecc_gen_privkey(ctx->curve_id, ctx->ndigits,
>  				       ctx->private_key);
>  
> -	memcpy(ctx->private_key, params.key, params.key_size);
> -	ecc_swap_digits(ctx->private_key, priv, ctx->ndigits);
> +	ecc_digits_from_bytes(params.key, params.key_size,
> +			      ctx->private_key, ctx->ndigits);
>  
>  	if (ecc_is_key_valid(ctx->curve_id, ctx->ndigits,
> -			     priv, params.key_size) < 0) {
> +			     ctx->private_key, params.key_size) < 0) {
>  		memzero_explicit(ctx->private_key, params.key_size);
>  		ret = -EINVAL;
>  	}
> -	memzero_explicit(priv, sizeof(priv));
>  
>  	return ret;
>  }
> diff --git a/include/crypto/internal/ecc.h b/include/crypto/internal/ecc.h
> index 4e2f5f938e91..7ca1f463d1ec 100644
> --- a/include/crypto/internal/ecc.h
> +++ b/include/crypto/internal/ecc.h
> @@ -103,7 +103,8 @@ int ecc_is_key_valid(unsigned int curve_id, unsigned int ndigits,
>   * Returns 0 if the private key was generated successfully, a negative value
>   * if an error occurred.
>   */
> -int ecc_gen_privkey(unsigned int curve_id, unsigned int ndigits, u64 *privkey);
> +int ecc_gen_privkey(unsigned int curve_id, unsigned int ndigits,
> +		    u64 *private_key);
>  
>  /**
>   * ecc_make_pub_key() - Compute an ECC public key

Acked-by: Jarkko Sakkinen <jarkko@kernel.org>

BR, Jarkko