Add crypto_box_seed_keypair like crypto_sign_seed_keypair

Uses sk = seed.

src/libsodium/crypto_box/crypto_box.c

@@ -1,6 +1,12 @@
 
 #include "crypto_box.h"
 
+size_t
+crypto_box_seedbytes(void)
+{
+    return crypto_box_SEEDBYTES;
+}
+
 size_t
 crypto_box_publickeybytes(void)
 {
@@ -49,6 +55,13 @@ crypto_box_primitive(void)
     return crypto_box_PRIMITIVE;
 }
 
+int
+crypto_box_seed_keypair(unsigned char *pk, unsigned char *sk,
+                        const unsigned char *seed)
+{
+    return crypto_box_curve25519xsalsa20poly1305_seed_keypair(pk, sk, seed);
+}
+
 int
 crypto_box_keypair(unsigned char *pk, unsigned char *sk)
 {

src/libsodium/crypto_box/curve25519xsalsa20poly1305/box_curve25519xsalsa20poly1305_api.c

@@ -1,5 +1,10 @@
 #include "crypto_box_curve25519xsalsa20poly1305.h"
 
+size_t
+crypto_box_curve25519xsalsa20poly1305_seedbytes(void) {
+    return crypto_box_curve25519xsalsa20poly1305_SEEDBYTES;
+}
+
 size_t
 crypto_box_curve25519xsalsa20poly1305_publickeybytes(void) {
     return crypto_box_curve25519xsalsa20poly1305_PUBLICKEYBYTES;

src/libsodium/crypto_box/curve25519xsalsa20poly1305/ref/api.h

@@ -3,10 +3,12 @@
 
 #define crypto_box crypto_box_curve25519xsalsa20poly1305
 #define crypto_box_open crypto_box_curve25519xsalsa20poly1305_open
+#define crypto_box_seed_keypair crypto_box_curve25519xsalsa20poly1305_seed_keypair
 #define crypto_box_keypair crypto_box_curve25519xsalsa20poly1305_keypair
 #define crypto_box_beforenm crypto_box_curve25519xsalsa20poly1305_beforenm
 #define crypto_box_afternm crypto_box_curve25519xsalsa20poly1305_afternm
 #define crypto_box_open_afternm crypto_box_curve25519xsalsa20poly1305_open_afternm
+#define crypto_box_SEEDBYTES crypto_box_curve25519xsalsa20poly1305_SEEDBYTES
 #define crypto_box_PUBLICKEYBYTES crypto_box_curve25519xsalsa20poly1305_PUBLICKEYBYTES
 #define crypto_box_SECRETKEYBYTES crypto_box_curve25519xsalsa20poly1305_SECRETKEYBYTES
 #define crypto_box_BEFORENMBYTES crypto_box_curve25519xsalsa20poly1305_BEFORENMBYTES

src/libsodium/crypto_box/curve25519xsalsa20poly1305/ref/keypair_curve25519xsalsa20poly1305.c

@@ -1,7 +1,19 @@
+#include <string.h>
+
 #include "crypto_scalarmult_curve25519.h"
 #include "api.h"
 #include "randombytes.h"
 
+int crypto_box_seed_keypair(
+  unsigned char *pk,
+  unsigned char *sk,
+  const unsigned char *seed
+)
+{
+  memmove(sk, seed, 32);
+  return crypto_scalarmult_curve25519_base(pk,sk);
+}
+
 int crypto_box_keypair(
   unsigned char *pk,
   unsigned char *sk

src/libsodium/include/sodium/crypto_box.h

@@ -20,6 +20,10 @@
 extern "C" {
 #endif
 
+#define crypto_box_SEEDBYTES crypto_box_curve25519xsalsa20poly1305_SEEDBYTES
+SODIUM_EXPORT
+size_t  crypto_box_seedbytes(void);
+
 #define crypto_box_PUBLICKEYBYTES crypto_box_curve25519xsalsa20poly1305_PUBLICKEYBYTES
 SODIUM_EXPORT
 size_t  crypto_box_publickeybytes(void);
@@ -52,6 +56,10 @@ size_t  crypto_box_macbytes(void);
 SODIUM_EXPORT
 const char *crypto_box_primitive(void);
 
+SODIUM_EXPORT
+int crypto_box_seed_keypair(unsigned char *pk, unsigned char *sk,
+                            const unsigned char *seed);
+
 SODIUM_EXPORT
 int crypto_box_keypair(unsigned char *pk, unsigned char *sk);
 

src/libsodium/include/sodium/crypto_box_curve25519xsalsa20poly1305.h

@@ -11,6 +11,10 @@
 extern "C" {
 #endif
 
+#define crypto_box_curve25519xsalsa20poly1305_SEEDBYTES 32U
+SODIUM_EXPORT
+size_t crypto_box_curve25519xsalsa20poly1305_seedbytes(void);
+
 #define crypto_box_curve25519xsalsa20poly1305_PUBLICKEYBYTES 32U
 SODIUM_EXPORT
 size_t crypto_box_curve25519xsalsa20poly1305_publickeybytes(void);
@@ -58,7 +62,13 @@ int crypto_box_curve25519xsalsa20poly1305_open(unsigned char *m,
                                                const unsigned char *sk);
 
 SODIUM_EXPORT
-int crypto_box_curve25519xsalsa20poly1305_keypair(unsigned char *pk, unsigned char *sk);
+int crypto_box_curve25519xsalsa20poly1305_seed_keypair(unsigned char *pk,
+                                                       unsigned char *sk,
+                                                       const unsigned char *seed);
+
+SODIUM_EXPORT
+int crypto_box_curve25519xsalsa20poly1305_keypair(unsigned char *pk,
+                                                  unsigned char *sk);
 
 SODIUM_EXPORT
 int crypto_box_curve25519xsalsa20poly1305_beforenm(unsigned char *k,