Add SSL_get_rc4_state.

This allows the current RC4 state of an SSL* to be extracted. We have
internal uses for this functionality.

Change-Id: Ic124c4b253c8325751f49e7a4c021768620ea4b7
Reviewed-on: https://boringssl-review.googlesource.com/3722
Reviewed-by: Adam Langley <agl@google.com>

include/openssl/aead.h

diff --git a/include/openssl/aead.h b/include/openssl/aead.h
index 8aedb1b..4b8f6cd 100644
--- a/include/openssl/aead.h
+++ b/include/openssl/aead.h
@@ -286,6 +286,14 @@
                                      const uint8_t *ad, size_t ad_len);
 
 
+/* Obscure functions. */
+
+/* EVP_AEAD_CTX_get_rc4_state sets |*out_key| to point to an RC4 key structure.
+ * It returns one on success or zero if |ctx| doesn't have an RC4 key. */
+OPENSSL_EXPORT int EVP_AEAD_CTX_get_rc4_state(const EVP_AEAD_CTX *ctx,
+                                              const RC4_KEY **out_key);
+
+
 #if defined(__cplusplus)
 }  /* extern C */
 #endif

include/openssl/base.h

diff --git a/include/openssl/base.h b/include/openssl/base.h
index 71223a0..37bca56 100644
--- a/include/openssl/base.h
+++ b/include/openssl/base.h
@@ -195,6 +195,7 @@
 typedef struct pkcs8_priv_key_info_st PKCS8_PRIV_KEY_INFO;
 typedef struct pkcs12_st PKCS12;
 typedef struct rand_meth_st RAND_METHOD;
+typedef struct rc4_key_st RC4_KEY;
 typedef struct rsa_meth_st RSA_METHOD;
 typedef struct rsa_st RSA;
 typedef struct sha256_state_st SHA256_CTX;

include/openssl/rc4.h

diff --git a/include/openssl/rc4.h b/include/openssl/rc4.h
index b5fc8ed..42a74f2 100644
--- a/include/openssl/rc4.h
+++ b/include/openssl/rc4.h
@@ -66,12 +66,10 @@
 
 /* RC4. */
 
-
-typedef struct rc4_key_st {
+struct rc4_key_st {
   uint32_t x, y;
   uint32_t data[256];
-} RC4_KEY;
-
+} /* RC4_KEY */;
 
 /* RC4_set_key performs an RC4 key schedule and initialises |rc4key| with |len|
  * bytes of key material from |key|. */

include/openssl/ssl.h

diff --git a/include/openssl/ssl.h b/include/openssl/ssl.h
index 82d632a..3d854a1 100644
--- a/include/openssl/ssl.h
+++ b/include/openssl/ssl.h
@@ -2253,6 +2253,12 @@
  * https://www.iana.org/assignments/tls-parameters/tls-parameters.xhtml#tls-parameters-4. */
 OPENSSL_EXPORT const SSL_CIPHER *SSL_get_cipher_by_value(uint16_t value);
 
+/* SSL_get_rc4_state sets |*read_key| and |*write_key| to the RC4 states for
+ * the read and write directions. It returns one on success or zero if |ssl|
+ * isn't using an RC4-based cipher suite. */
+OPENSSL_EXPORT int SSL_get_rc4_state(const SSL *ssl, const RC4_KEY **read_key,
+                                     const RC4_KEY **write_key);
+
 
 /* Android compatibility section.
  *