diff --git a/CMakeLists.txt b/CMakeLists.txt
index 31eb67575f..e977f725a3 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -13,6 +13,7 @@ set(SOURCES
     ed25519-donna/ed25519.c ed25519-donna/curve25519-donna-scalarmult-base.c ed25519-donna/ed25519-sha3.c ed25519-donna/ed25519-keccak.c
     blake2b.c blake2s.c
     chacha20poly1305/chacha20poly1305.c chacha20poly1305/chacha_merged.c chacha20poly1305/poly1305-donna.c chacha20poly1305/rfc7539.c
+    rc4.c
 )
 
 add_library(TrezorCrypto STATIC ${SOURCES})
diff --git a/Makefile b/Makefile
index 6f1051b412..d83725ebf4 100644
--- a/Makefile
+++ b/Makefile
@@ -48,6 +48,7 @@ SRCS  += ed25519-donna/ed25519-donna-basepoint-table.c ed25519-donna/ed25519-don
 SRCS  += ed25519-donna/ed25519.c ed25519-donna/curve25519-donna-scalarmult-base.c ed25519-donna/ed25519-sha3.c ed25519-donna/ed25519-keccak.c
 SRCS  += blake2b.c blake2s.c
 SRCS  += chacha20poly1305/chacha20poly1305.c chacha20poly1305/chacha_merged.c chacha20poly1305/poly1305-donna.c chacha20poly1305/rfc7539.c
+SRCS  += rc4.c
 
 OBJS   = $(SRCS:.c=.o)
 
diff --git a/rc4.c b/rc4.c
new file mode 100644
index 0000000000..db9eb1ffa7
--- /dev/null
+++ b/rc4.c
@@ -0,0 +1,56 @@
+/**
+ * Copyright (c) 2017 Saleem Rashid
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included
+ * in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, E1PRESS
+ * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES
+ * OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#include "rc4.h"
+
+static inline void rc4_swap(RC4_CTX *ctx, uint8_t i, uint8_t j) {
+    uint8_t temp = ctx->S[i];
+    ctx->S[i] = ctx->S[j];
+    ctx->S[j] = temp;
+}
+
+void rc4_init(RC4_CTX *ctx, const uint8_t *key, size_t length) {
+    ctx->i = 0;
+    ctx->j = 0;
+
+    for (size_t i = 0; i < 256; i++) {
+	ctx->S[i] = i;
+    }
+
+    uint8_t j = 0;
+    for (size_t i = 0; i < 256; i++) {
+	j += ctx->S[i] + key[i % length];
+	rc4_swap(ctx, i, j);
+    }
+}
+
+void rc4_encrypt(RC4_CTX *ctx, uint8_t *buffer, size_t length) {
+    for (size_t idx = 0; idx < length; idx++) {
+	ctx->i++;
+	ctx->j += ctx->S[ctx->i];
+
+	rc4_swap(ctx, ctx->i, ctx->j);
+
+	uint8_t K = ctx->S[(ctx->S[ctx->i] + ctx->S[ctx->j]) % 256];
+	buffer[idx] ^= K;
+    }
+}
diff --git a/rc4.h b/rc4.h
new file mode 100644
index 0000000000..7b56e4a3d0
--- /dev/null
+++ b/rc4.h
@@ -0,0 +1,37 @@
+/**
+ * Copyright (c) 2017 Saleem Rashid
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included
+ * in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+ * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES
+ * OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#ifndef __RC4_H__
+#define __RC4_H__
+
+#include <stdint.h>
+#include <stddef.h>
+
+typedef struct {
+    uint8_t S[256];
+    uint8_t i, j;
+} RC4_CTX;
+
+void rc4_init(RC4_CTX *ctx, const uint8_t *key, size_t length);
+void rc4_encrypt(RC4_CTX *ctx, uint8_t *buffer, size_t length);
+
+#endif