[PATCH v4 01/30] crypto: des/3des_ede - add new helpers to verify keys

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

The recently added helper routine to perform key strength validation
of triple DES keys is slightly inadequate, since it comes in two versions,
neither of which are highly useful for anything other than skciphers (and
many drivers still use the older blkcipher interfaces).

So let's add a new helper and, considering that this is a helper function
that is only intended to be used by crypto code itself, put it in a new
des.h header under crypto/internal.

While at it, implement a similar helper for single DES, so that we can
start replacing the pattern of calling des_ekey() into a temp buffer
that occurs in many drivers in drivers/crypto.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
 crypto/des_generic.c          | 13 ---
 include/crypto/internal/des.h | 95 ++++++++++++++++++++
 2 files changed, 95 insertions(+), 13 deletions(-)

diff --git a/crypto/des_generic.c b/crypto/des_generic.c
index dc085514408a..c4d8ecda4ddf 100644
--- a/crypto/des_generic.c
+++ b/crypto/des_generic.c
@@ -841,19 +841,6 @@ static void des_decrypt(struct crypto_tfm *tfm, u8 *dst, const u8 *src)
 	d[1] = cpu_to_le32(L);
 }
 
-/*
- * RFC2451:
- *
- *   For DES-EDE3, there is no known need to reject weak or
- *   complementation keys.  Any weakness is obviated by the use of
- *   multiple keys.
- *
- *   However, if the first two or last two independent 64-bit keys are
- *   equal (k1 == k2 or k2 == k3), then the DES3 operation is simply the
- *   same as DES.  Implementers MUST reject keys that exhibit this
- *   property.
- *
- */
 int __des3_ede_setkey(u32 *expkey, u32 *flags, const u8 *key,
 		      unsigned int keylen)
 {
diff --git a/include/crypto/internal/des.h b/include/crypto/internal/des.h
new file mode 100644
index 000000000000..aad576bad8ad
--- /dev/null
+++ b/include/crypto/internal/des.h
@@ -0,0 +1,95 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * DES & Triple DES EDE key verification helpers
+ */
+
+#ifndef __CRYPTO_INTERNAL_DES_H
+#define __CRYPTO_INTERNAL_DES_H
+
+#include <linux/crypto.h>
+#include <linux/fips.h>
+#include <crypto/des.h>
+
+/**
+ * crypto_des_verify_key - Check whether a DES is weak
+ * @tfm: the crypto algo
+ * @key: the key buffer
+ *
+ * Returns -EINVAL if the key is weak and the crypto TFM does not permit weak
+ * keys. Otherwise, 0 is returned.
+ *
+ * It is the job of the caller to ensure that the size of the key equals
+ * DES_KEY_SIZE.
+ */
+static inline int crypto_des_verify_key(struct crypto_tfm *tfm, const u8 *key)
+{
+	u32 tmp[DES_EXPKEY_WORDS];
+	int err = 0;
+
+	if (!(crypto_tfm_get_flags(tfm) & CRYPTO_TFM_REQ_FORBID_WEAK_KEYS))
+		return 0;
+
+	if (!des_ekey(tmp, key)) {
+		crypto_tfm_set_flags(tfm, CRYPTO_TFM_RES_WEAK_KEY);
+		err = -EINVAL;
+	}
+
+	memzero_explicit(tmp, sizeof(tmp));
+	return err;
+}
+
+/*
+ * RFC2451:
+ *
+ *   For DES-EDE3, there is no known need to reject weak or
+ *   complementation keys.  Any weakness is obviated by the use of
+ *   multiple keys.
+ *
+ *   However, if the first two or last two independent 64-bit keys are
+ *   equal (k1 == k2 or k2 == k3), then the DES3 operation is simply the
+ *   same as DES.  Implementers MUST reject keys that exhibit this
+ *   property.
+ *
+ */
+
+/**
+ * crypto_des3_ede_verify_key - Check whether a DES3-EDE is weak
+ * @tfm: the crypto algo
+ * @key: the key buffer
+ *
+ * Returns -EINVAL if the key is weak and the crypto TFM does not permit weak
+ * keys or when running in FIPS mode. Otherwise, 0 is returned. Note that some
+ * keys are rejected in FIPS mode even if weak keys are permitted by the TFM
+ * flags.
+ *
+ * It is the job of the caller to ensure that the size of the key equals
+ * DES3_EDE_KEY_SIZE.
+ */
+static inline int crypto_des3_ede_verify_key(struct crypto_tfm *tfm,
+					     const u8 *key)
+{
+	int err = -EINVAL;
+	u32 K[6];
+
+	memcpy(K, key, DES3_EDE_KEY_SIZE);
+
+	if ((!((K[0] ^ K[2]) | (K[1] ^ K[3])) ||
+	     !((K[2] ^ K[4]) | (K[3] ^ K[5]))) &&
+	    (fips_enabled || (crypto_tfm_get_flags(tfm) &
+		              CRYPTO_TFM_REQ_FORBID_WEAK_KEYS)))
+		goto bad;
+
+	if ((!((K[0] ^ K[4]) | (K[1] ^ K[5]))) && fips_enabled)
+		goto bad;
+
+	err = 0;
+out:
+	memzero_explicit(K, DES3_EDE_KEY_SIZE);
+	return err;
+
+bad:
+	crypto_tfm_set_flags(tfm, CRYPTO_TFM_RES_WEAK_KEY);
+	goto out;
+}
+
+#endif /* __CRYPTO_INTERNAL_DES_H */
-- 
2.17.1