crypto: doc - add KPP documentation

Add the KPP API documentation to the kernel crypto API Sphinx
documentation. This addition includes the documentation of the
ECDH and DH helpers which are needed to create the approrpiate input
data for the crypto_kpp_set_secret function.

Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

1 files changed, 58 insertions, 0 deletions

diff --git a/include/crypto/ecdh.h b/include/crypto/ecdh.h
index 84bad548d194..03a64f62ba7a 100644
--- a/include/crypto/ecdh.h
+++ b/include/crypto/ecdh.h
@@ -13,18 +13,76 @@
 #ifndef _CRYPTO_ECDH_
 #define _CRYPTO_ECDH_
 
+/**
+ * DOC: ECDH Helper Functions
+ *
+ * To use ECDH with the KPP cipher API, the following data structure and
+ * functions should be used.
+ *
+ * The ECC curves known to the ECDH implementation are specified in this
+ * header file.
+ *
+ * To use ECDH with KPP, the following functions should be used to operate on
+ * an ECDH private key. The packet private key that can be set with
+ * the KPP API function call of crypto_kpp_set_secret.
+ */
+
 /* Curves IDs */
 #define ECC_CURVE_NIST_P192	0x0001
 #define ECC_CURVE_NIST_P256	0x0002
 
+/**
+ * struct ecdh - define an ECDH private key
+ *
+ * @curve_id:	ECC curve the key is based on.
+ * @key:	Private ECDH key
+ * @key_size:	Size of the private ECDH key
+ */
 struct ecdh {
 	unsigned short curve_id;
 	char *key;
 	unsigned short key_size;
 };
 
+/**
+ * crypto_ecdh_key_len() - Obtain the size of the private ECDH key
+ * @params:	private ECDH key
+ *
+ * This function returns the packet ECDH key size. A caller can use that
+ * with the provided ECDH private key reference to obtain the required
+ * memory size to hold a packet key.
+ *
+ * Return: size of the key in bytes
+ */
 int crypto_ecdh_key_len(const struct ecdh *params);
+
+/**
+ * crypto_ecdh_encode_key() - encode the private key
+ * @buf:	Buffer allocated by the caller to hold the packet ECDH
+ *		private key. The buffer should be at least crypto_ecdh_key_len
+ *		bytes in size.
+ * @len:	Length of the packet private key buffer
+ * @p:		Buffer with the caller-specified private key
+ *
+ * The ECDH implementations operate on a packet representation of the private
+ * key.
+ *
+ * Return:	-EINVAL if buffer has insufficient size, 0 on success
+ */
 int crypto_ecdh_encode_key(char *buf, unsigned int len, const struct ecdh *p);
+
+/**
+ * crypto_ecdh_decode_key() - decode a private key
+ * @buf:	Buffer holding a packet key that should be decoded
+ * @len:	Lenth of the packet private key buffer
+ * @p:		Buffer allocated by the caller that is filled with the
+ *		unpacket ECDH private key.
+ *
+ * The unpacking obtains the private key by pointing @p to the correct location
+ * in @buf. Thus, both pointers refer to the same memory.
+ *
+ * Return:	-EINVAL if buffer has insufficient size, 0 on success
+ */
 int crypto_ecdh_decode_key(const char *buf, unsigned int len, struct ecdh *p);
 
 #endif