diff --git a/src/common/crypto/EmuRsa.cpp b/src/common/crypto/EmuRsa.cpp
index a86eaa983..38616e123 100644
--- a/src/common/crypto/EmuRsa.cpp
+++ b/src/common/crypto/EmuRsa.cpp
@@ -18,6 +18,7 @@
 // *  59 Temple Place - Suite 330, Bostom, MA 02111-1307, USA.
 // *
 // *  (c) 2018 ergo720
+// *  (c) 2019 Jannik Vogel
 // *
 // *  All rights reserved
 // *
@@ -102,7 +103,7 @@ double*			sinCos = NULL;
 
 /* Global function declarations */
 giant newgiant(int numshorts);
-void gigimport(giant g, unsigned char* buff, int len);
+void gigimport(giant g, const unsigned char* buff, int len);
 void auxmulg(giant a, giant b);
 void normal_subg(giant a, giant b);
 void reverse_subg(giant a, giant b);
@@ -151,27 +152,27 @@ void iaddg(int i, giant g); /* g += i, with i non-negative and < 2^16. */
 int gsign(giant g); /* Returns the sign of g: -1, 0, 1. */
 void absg(giant g); /* g := |g|. */
 
-
-void RSAdecrypt(unsigned char* c_number, unsigned char* cryptbuffer, RSA_PUBLIC_KEY key)
+void ModExp(unsigned char* a_number, const unsigned char* b_number, unsigned int b_len, const unsigned char* c_number, unsigned int c_len, const unsigned char* d_number, unsigned int d_len)
 {
-	giant n = newgiant(GIANT_INFINITY);
-	giant e = newgiant(GIANT_INFINITY);
-	giant sig = newgiant(GIANT_INFINITY);
+	giant b = newgiant(GIANT_INFINITY);
+	giant c = newgiant(GIANT_INFINITY);
+	giant d = newgiant(GIANT_INFINITY);
+	gigimport(b, b_number, b_len);
+	gigimport(c, c_number, c_len);
+	gigimport(d, d_number, d_len);
 
-	gigimport(sig, c_number, 256);
+	/* a = b := b^c (mod d). */
+	powermodg(b, c, d);
 
-	gigimport(n, key.KeyData.Modulus, 256);
-
-	gigimport(e, key.KeyData.Exponent, 4);
-
-	/* x := x^n (mod z). */
-	powermodg(sig, e, n);
-
-	memset(cryptbuffer, 0x00, 256);
-	memcpy(cryptbuffer, sig->n, 256);
+	memcpy(a_number, b->n, d_len);
 }
 
-bool Verifyhash(unsigned char* hash, unsigned char* decryptBuffer, RSA_PUBLIC_KEY key)
+void RSAdecrypt(const unsigned char* c_number, unsigned char* cryptbuffer, RSA_PUBLIC_KEY key)
+{
+	ModExp(cryptbuffer, c_number, 256, key.KeyData.Exponent, 4, key.KeyData.Modulus, 256);
+}
+
+bool Verifyhash(const unsigned char* hash, const unsigned char* decryptBuffer, RSA_PUBLIC_KEY key)
 {
 	unsigned char cmphash[20];
 	int a;
@@ -236,20 +237,21 @@ giant newgiant(int numshorts)
 	return(thegiant);
 }
 
-// ergo720: there's a bug in the original implementation of gigimport that prevents the rsa algorithm from working correctly on Windows (but
-// for some reason it works on Ubuntu). This replacement implementation is taken from
-// http://xbox-linux-devel.narkive.com/Qw6o31DP/xbedump-fix-for-array-out-of-bounds-access#post1
-// and it has been improved based on JayFoxRox suggestions. See the link below for the details
-// https://github.com/xqemu/xbedump/pull/5
-void gigimport(giant g, unsigned char *buff, int len) {
+void gigimport(giant g, const unsigned char *buff, int len) {
 
 	// copy buffered 'number' into giant's number buffer
 	memcpy(g->n, buff, len);
 
 	assert((len % 2) == 0);
 
+	// Get number of shorts
 	g->sign = len / 2;
 
+	// Only count used shorts
+	while((g->sign >= 1) && (g->n[g->sign - 1] == 0)) {
+		g->sign -= 1;
+	}
+
 	assert(g->sign != 0);
 }
 
diff --git a/src/common/crypto/EmuRsa.h b/src/common/crypto/EmuRsa.h
index 6b67181ac..01204a3a7 100644
--- a/src/common/crypto/EmuRsa.h
+++ b/src/common/crypto/EmuRsa.h
@@ -47,7 +47,8 @@ typedef struct _RSA_PUBLIC_KEY
 
 #pragma pack()
 
-void RSAdecrypt(unsigned char* c_number, unsigned char* cryptbuffer, RSA_PUBLIC_KEY key);
-bool Verifyhash(unsigned char* hash, unsigned char* decryptBuffer, RSA_PUBLIC_KEY key);
+void ModExp(unsigned char* a_number, const unsigned char* b_number, unsigned int b_len, const unsigned char* c_number, unsigned int c_len, const unsigned char* d_number, unsigned int d_len);
+void RSAdecrypt(const unsigned char* c_number, unsigned char* cryptbuffer, RSA_PUBLIC_KEY key);
+bool Verifyhash(const unsigned char* hash, const unsigned char* decryptBuffer, RSA_PUBLIC_KEY key);
 
 #endif
diff --git a/src/core/kernel/exports/EmuKrnlXc.cpp b/src/core/kernel/exports/EmuKrnlXc.cpp
index 8fe303bc1..2d305ab61 100644
--- a/src/core/kernel/exports/EmuKrnlXc.cpp
+++ b/src/core/kernel/exports/EmuKrnlXc.cpp
@@ -20,7 +20,8 @@
 // *  59 Temple Place - Suite 330, Bostom, MA 02111-1307, USA.
 // *
 // *  (c) 2002-2003 Aaron Robinson <caustik@caustik.com>
-// *  (c) 2016 Patrick van Logchem <pvanlogchem@gmail.com>
+// *  (c) 2016 Patrick van Logchem <pvanlogchem@gmail.com>
+// *  (c) 2019 Jannik Vogel
 // *
 // *  All rights reserved
 // *
@@ -40,6 +41,7 @@ namespace xboxkrnl
 #include "common\crypto\EmuSha.h" // For A_SHAInit, etc.
 #include "common\crypto\LibRc4.h" // For RC4 Functions
 #include "common\crypto\EmuDes.h" // For DES Functions
+#include "common\crypto\EmuRSA.h" // For RSA Functions
 
 // prevent name collisions
 namespace NtDll
@@ -212,9 +214,10 @@ xboxkrnl::ULONG NTAPI JumpedModExp
 	xboxkrnl::ULONG dwN
 )
 {
-	ULONG ret = 0;
-
-	LOG_UNIMPLEMENTED();
+	ULONG ret = 1;
+
+	unsigned int len = dwN * 4;
+	ModExp((unsigned char*)pA, (const unsigned char*)pB, len, (const unsigned char*)pC, len, (const unsigned char*)pD, len);
 
 	return ret;
 }