diff --git a/crypto/encoding/base16.c b/crypto/encoding/base16.c
index bc9b8b4..17d2dcd 100644
--- a/crypto/encoding/base16.c
+++ b/crypto/encoding/base16.c
@@ -22,7 +22,7 @@ int libp2p_crypto_encoding_base16_encode(const unsigned char* incoming, size_t i
 	*results_length = 0;
 	for(int i = 0; i < incoming_length; i++) {
 		unsigned char buf[3];
-		sprintf(buf, "%02x", incoming[i]);
+		sprintf((char*)buf, "%02x", incoming[i]);
 		results[i * 2] = buf[0];
 		results[i * 2 + 1] = buf[1];
 		*results_length += 2;
@@ -56,7 +56,7 @@ int libp2p_crypto_encoding_base16_decode(const unsigned char* incoming, size_t i
 
 	memset(results, 0, *results_length);
 
-	unsigned char* pos = (char*)incoming;
+	char* pos = (char*)incoming;
 
 	for(int i = 0; i < incoming_length / 2; i++) {
 		sscanf(pos, "%2hhx", &results[i]);
diff --git a/crypto/encoding/base32.c b/crypto/encoding/base32.c
index b11a35f..bc8d407 100644
--- a/crypto/encoding/base32.c
+++ b/crypto/encoding/base32.c
@@ -637,9 +637,9 @@ base32_decode_alloc_ctx (struct base32_decode_context *ctx,
 int libp2p_crypto_encoding_base32_encode(const unsigned char* incoming, size_t incoming_length,
 		unsigned char* results, size_t* results_length) {
 	memset(results, 0, *results_length);
-	base32_encode(incoming, incoming_length, results, *results_length);
+	base32_encode((char*)incoming, incoming_length, (char*)results, *results_length);
 	if (results[ (*results_length) -1] == 0)
-		*results_length = strlen(results);
+		*results_length = strlen((char*)results);
 	return 1;
 }
 
@@ -664,7 +664,7 @@ size_t libp2p_crypto_encoding_base32_encode_size(size_t incoming_length) {
  */
 int libp2p_crypto_encoding_base32_decode(const unsigned char* incoming, size_t incoming_length,
 		unsigned char* results, size_t* results_length) {
-	int retVal = base32_decode_ctx(NULL, incoming, incoming_length, results, results_length);
+	int retVal = base32_decode_ctx(NULL, (char*)incoming, incoming_length, (char*)results, results_length);
 
 	// unknown error
 	if (results == NULL)
diff --git a/crypto/rsa.c b/crypto/rsa.c
index e2fd9ef..e60bdcd 100644
--- a/crypto/rsa.c
+++ b/crypto/rsa.c
@@ -2,6 +2,7 @@
 #include <string.h>
 
 #include "libp2p/crypto/rsa.h"
+#include "libp2p/crypto/sha256.h"
 
 // mbedtls stuff
 #include "mbedtls/config.h"
@@ -187,7 +188,7 @@ int libp2p_crypto_rsa_private_key_fill_public_key(struct RsaPrivateKey* private_
 	// first build the rsa context
 	mbedtls_pk_context ctx;
 	mbedtls_pk_init(&ctx);
-	mbedtls_pk_parse_key(&ctx, private_key->der, private_key->der_length, NULL, 0);
+	mbedtls_pk_parse_key(&ctx, (unsigned char*)private_key->der, private_key->der_length, NULL, 0);
 
 	// buffer
 	size_t buffer_size = 1600;
@@ -227,3 +228,30 @@ int libp2p_crypto_rsa_rsa_private_key_free(struct RsaPrivateKey* private_key) {
 	return 1;
 }
 
+/**
+ * sign a message
+ * @param private_key the private key
+ * @param message the message to be signed
+ * @param message_length the length of message
+ * @param result the resultant signature. Note: should be pre-allocated and be the size of the private key (i.e. 2048)
+ * @returns true(1) on successs, otherwise false(0)
+ */
+int libp2p_crypto_rsa_sign(struct RsaPrivateKey* private_key, unsigned char* message, size_t message_length, unsigned char* result) {
+	unsigned char output[32];
+	libp2p_crypto_hashing_sha256(message, message_length, output);
+
+	mbedtls_rsa_context ctx;
+	mbedtls_ctr_drbg_context ctr_drbg;
+	mbedtls_rsa_init(&ctx, MBEDTLS_RSA_PKCS_V15, 0);
+	mbedtls_ctr_drbg_init(&ctr_drbg);
+	int retVal = mbedtls_rsa_rsassa_pkcs1_v15_sign( &ctx,
+			mbedtls_ctr_drbg_random,
+			&ctr_drbg,
+			MBEDTLS_RSA_PRIVATE,
+			MBEDTLS_MD_SHA256,
+            32,
+            output,
+            result );
+	return retVal == 0;
+}
+
diff --git a/include/libp2p/crypto/rsa.h b/include/libp2p/crypto/rsa.h
index 24ae22f..1307f73 100644
--- a/include/libp2p/crypto/rsa.h
+++ b/include/libp2p/crypto/rsa.h
@@ -45,4 +45,14 @@ int libp2p_crypto_rsa_private_key_fill_public_key(struct RsaPrivateKey* private_
  */
 int libp2p_crypto_rsa_rsa_private_key_free(struct RsaPrivateKey* private_key);
 
+/**
+ * sign a message
+ * @param private_key the private key
+ * @param message the message to be signed
+ * @param message_length the length of message
+ * @param result the resultant signature. Note: should be pre-allocated and be the size of the private key (i.e. 2048)
+ * @returns true(1) on successs, otherwise false(0)
+ */
+int libp2p_crypto_rsa_sign(struct RsaPrivateKey* private_key, unsigned char* message, size_t message_length, unsigned char* result);
+
 #endif /* rsa_h */
diff --git a/test/crypto/test_base58.h b/test/crypto/test_base58.h
index 9c4f7ab..59a837f 100644
--- a/test/crypto/test_base58.h
+++ b/test/crypto/test_base58.h
@@ -77,7 +77,7 @@ int test_base58_peer_address() {
 	unsigned char* ptr_to_result = result_buffer;
 	memset(result_buffer, 0, result_buffer_length);
 	// now get the decoded address
-	int return_value = libp2p_crypto_encoding_base58_decode(x_data, x_data_length, &ptr_to_result, &result_buffer_length);
+	int return_value = libp2p_crypto_encoding_base58_decode((unsigned char*)x_data, x_data_length, &ptr_to_result, &result_buffer_length);
 	if (return_value == 0)
 		return 0;
 	// add 2 bytes to the front for the varint
diff --git a/test/crypto/test_rsa.h b/test/crypto/test_rsa.h
index 7c8075a..e8098af 100644
--- a/test/crypto/test_rsa.h
+++ b/test/crypto/test_rsa.h
@@ -135,7 +135,7 @@ int test_crypto_rsa_public_key_to_peer_id() {
 	memset(decode_base64, 0, decode_base64_size);
 	unsigned char* ptr = decode_base64;
 
-	int retVal = libp2p_crypto_encoding_base64_decode(orig_priv_key, strlen(orig_priv_key), ptr, decode_base64_size, &decode_base64_size);
+	int retVal = libp2p_crypto_encoding_base64_decode((unsigned char*)orig_priv_key, strlen(orig_priv_key), ptr, decode_base64_size, &decode_base64_size);
 	if (retVal == 0)
 		return 0;
 
@@ -158,7 +158,7 @@ int test_crypto_rsa_public_key_to_peer_id() {
 
 	// 3) grab the public key, hash it, then base58 it
 	unsigned char hashed[32];
-	ID_FromPK_non_null_terminated(hashed, private_key.public_key_der, private_key.public_key_length);
+	ID_FromPK_non_null_terminated((char*)hashed, (unsigned char*)private_key.public_key_der, private_key.public_key_length);
 	size_t final_id_size = 1600;
 	unsigned char final_id[final_id_size];
 	memset(final_id, 0, final_id_size);
@@ -170,7 +170,7 @@ int test_crypto_rsa_public_key_to_peer_id() {
 	if (orig_peer_id_size != final_id_size)
 		return 0;
 
-	if (strncmp(orig_peer_id, final_id, final_id_size) != 0)
+	if (strncmp(orig_peer_id, (char*)final_id, final_id_size) != 0)
 		return 0;
 
 	return 1;