diff --git a/Makefile b/Makefile
index 27db3664..f6b156e5 100644
--- a/Makefile
+++ b/Makefile
@@ -149,8 +149,8 @@ gdb_firmware: $(FIRMWARE_BUILD_DIR)/firmware.elf ## start remote gdb session to
 ## misc commands:
 
 vendorheader: ## construct default vendor header
-	./tools/build_vendorheader 'e28a8970753332bd72fef413e6b0b2ef1b4aadda7aa2c141f233712a6876b351:d4eec1869fb1b8a4e817516ad5a931557cb56805c3eb16e8f3a803d647df7869:772c8a442b7db06e166cfbc1ccbcbcde6f3eba76a4e98ef3ffc519502237d6ef' 1 0.0 SatoshiLabs assets/satoshilabs_120.toif embed/firmware/vendorheader.bin
-	./tools/binctl embed/firmware/vendorheader.bin -s 1 4444444444444444444444444444444444444444444444444444444444444444
+	./tools/build_vendorheader 'e28a8970753332bd72fef413e6b0b2ef1b4aadda7aa2c141f233712a6876b351:d4eec1869fb1b8a4e817516ad5a931557cb56805c3eb16e8f3a803d647df7869:772c8a442b7db06e166cfbc1ccbcbcde6f3eba76a4e98ef3ffc519502237d6ef' 2 0.0 DEVEL assets/vendor_devel.toif embed/firmware/vendorheader.bin
+	./tools/binctl embed/firmware/vendorheader.bin -s 1:2 4444444444444444444444444444444444444444444444444444444444444444:4545454545454545454545454545454545454545454545454545454545454545
 
 binctl: ## print info about binary files
 	./tools/binctl $(BOOTLOADER_BUILD_DIR)/bootloader.bin
diff --git a/SConscript.bootloader b/SConscript.bootloader
index 42e2137f..5674a2a4 100644
--- a/SConscript.bootloader
+++ b/SConscript.bootloader
@@ -169,5 +169,5 @@ program_bin = env.Command(
     source=program_elf,
     action=[
         '$OBJCOPY -O binary -j .header -j .flash -j .data $SOURCE $TARGET',
-        '$BINCTL $TARGET -s 1 4141414141414141414141414141414141414141414141414141414141414141',
+        '$BINCTL $TARGET -s 1:2 4141414141414141414141414141414141414141414141414141414141414141:4242424242424242424242424242424242424242424242424242424242424242',
     ], )
diff --git a/SConscript.firmware b/SConscript.firmware
index 944fdb9d..3b0eed04 100644
--- a/SConscript.firmware
+++ b/SConscript.firmware
@@ -434,7 +434,7 @@ program_bin = env.Command(
     source=program_elf,
     action=[
         '$OBJCOPY -O binary -j .header -j .flash -j .data $SOURCE $TARGET',
-        '$BINCTL $TARGET -s 1 4747474747474747474747474747474747474747474747474747474747474747',
+        '$BINCTL $TARGET -s 1:2 4747474747474747474747474747474747474747474747474747474747474747:4848484848484848484848484848484848484848484848484848484848484848',
     ], )
 
 program0_bin = env.Command(
diff --git a/assets/satoshilabs_120.toif b/assets/satoshilabs_120.toif
deleted file mode 100644
index e7711ba0..00000000
Binary files a/assets/satoshilabs_120.toif and /dev/null differ
diff --git a/assets/vendor_devel.png b/assets/vendor_devel.png
new file mode 100644
index 00000000..9014bddd
Binary files /dev/null and b/assets/vendor_devel.png differ
diff --git a/assets/vendor_devel.toif b/assets/vendor_devel.toif
new file mode 100644
index 00000000..e4867104
Binary files /dev/null and b/assets/vendor_devel.toif differ
diff --git a/embed/boardloader/main.c b/embed/boardloader/main.c
index 64746133..a0bc8626 100644
--- a/embed/boardloader/main.c
+++ b/embed/boardloader/main.c
@@ -104,7 +104,7 @@ bool copy_sdcard(void)
     return true;
 }
 
-const uint8_t BOARDLOADER_KEY_M = 1;
+const uint8_t BOARDLOADER_KEY_M = 2;
 const uint8_t BOARDLOADER_KEY_N = 3;
 static const uint8_t * const BOARDLOADER_KEYS[] = {
     (const uint8_t *)"\xdb\x99\x5f\xe2\x51\x69\xd1\x41\xca\xb9\xbb\xba\x92\xba\xa0\x1f\x9f\x2e\x1e\xce\x7d\xf4\xcb\x2a\xc0\x51\x90\xf3\x7f\xcc\x1f\x9d",
diff --git a/embed/bootloader/main.c b/embed/bootloader/main.c
index 451c7770..05f90ab5 100644
--- a/embed/bootloader/main.c
+++ b/embed/bootloader/main.c
@@ -47,7 +47,7 @@ void display_vendor(const uint8_t *vimg, const char *vstr, uint32_t vstr_len, ui
     display_refresh();
 }
 
-const uint8_t BOOTLOADER_KEY_M = 1;
+const uint8_t BOOTLOADER_KEY_M = 2;
 const uint8_t BOOTLOADER_KEY_N = 3;
 static const uint8_t * const BOOTLOADER_KEYS[] = {
     (const uint8_t *)"\xd7\x59\x79\x3b\xbc\x13\xa2\x81\x9a\x82\x7c\x76\xad\xb6\xfb\xa8\xa4\x9a\xee\x00\x7f\x49\xf2\xd0\x99\x2d\x99\xb8\x25\xad\x2c\x48",
diff --git a/tools/binctl b/tools/binctl
index bb3b8fb9..e6571d9c 100755
--- a/tools/binctl
+++ b/tools/binctl
@@ -8,16 +8,36 @@ import binascii
 import pyblake2
 
 import ed25519raw
+import ed25519cosi
 
 
 def sign_data(seckeys, data):
+    digest = pyblake2.blake2s(data).digest()
     if len(seckeys) == 1:
         sk = seckeys[0]
         pk = ed25519raw.publickey(sk)
-        digest = pyblake2.blake2s(data).digest()
         return ed25519raw.signature(digest, sk, pk)
     else:
-        raise NotImplementedError
+        pubkeys = [ed25519raw.publickey(sk) for sk in seckeys]
+        ctr = 0
+        nonces = []
+        commits = []
+        for sk in seckeys:
+            r, R = ed25519cosi.get_nonce(sk, digest, ctr)
+            nonces.append(r)
+            commits.append(R)
+        global_pk = ed25519cosi.combine_keys(pubkeys)
+        global_R = ed25519cosi.combine_keys(commits)
+        sigs = []
+        for sk, r, R in zip(seckeys, nonces, commits):
+            h = ed25519raw.H(sk)
+            b = ed25519raw.b
+            a = 2**(b - 2) + sum(2**i * ed25519raw.bit(h, i) for i in range(3, b - 2))
+            S = (r + ed25519raw.Hint(global_R + global_pk + digest) * a) % ed25519raw.l
+            sigs.append(ed25519raw.encodeint(S))
+        sig = ed25519cosi.combine_sig(global_R, sigs)
+        ed25519raw.checkvalid(sig, digest, global_pk)
+        return sig
 
 
 def format_sigmask(sigmask):
@@ -186,6 +206,14 @@ class VendorHeader(object):
         return header
 
     def sign(self, sigmask, seckeys):
+        # check whether provided arguments match vsig_m/vsig_n
+        if len(seckeys) != self.vsig_m:
+            raise Exception('invalid number of signatures (vsig_m expected %d, got %d)' % (self.vsig_m, len(seckeys)))
+        if sigmask >= (1 << self.vsig_n):
+            raise Exception('signature index is higher than vsig_n (%d)' % self.vsig_n)
+        if bin(sigmask).count('1') != self.vsig_m:
+            raise Exception('invalid number of indexes (vsig_m expected %d, got %d)' % (self.vsig_m, bin(sigmask).count('1')))
+        # sign
         header = self.serialize_header(sig=False)
         self.sigmask = sigmask
         self.sig = sign_data(seckeys, header)
@@ -224,7 +252,7 @@ def main():
         sigmask = 0
         if ':' in sys.argv[3]:
             for idx in sys.argv[3].split(':'):
-                sigmask = 1 << (int(idx) - 1)
+                sigmask |= 1 << (int(idx) - 1)
         else:
             sigmask = 1 << (int(sys.argv[3]) - 1)
         if ':' in sys.argv[4]:
diff --git a/tools/ed25519cosi.py b/tools/ed25519cosi.py
index a056c483..9b4317b2 100644
--- a/tools/ed25519cosi.py
+++ b/tools/ed25519cosi.py
@@ -220,17 +220,17 @@ def test(data):
         sks.append(seckey)
         pks.append(pubkey)
         ctr = 0
-        (r, R) = get_nonce(seckey, digest, ctr)
+        r, R = get_nonce(seckey, digest, ctr)
         print('Local nonce:  %s' % hex(ed25519raw.encodeint(r)))
         print('Local commit: %s' % hex(R))
         nonces.append(r)
         commits.append(R)
 
-    globalPk = combine_keys([pks[i] for i in keyset])
-    globalR = combine_keys([commits[i] for i in keyset])
+    global_pk = combine_keys([pks[i] for i in keyset])
+    global_R = combine_keys([commits[i] for i in keyset])
     print('-----------------')
-    print('Global pubkey: %s' % hex(globalPk))
-    print('Global commit: %s' % hex(globalR))
+    print('Global pubkey: %s' % hex(global_pk))
+    print('Global commit: %s' % hex(global_R))
     print('-----------------')
 
     for i in range(0, N):
@@ -240,17 +240,15 @@ def test(data):
         R = commits[i]
         h = ed25519raw.H(seckey)
         b = ed25519raw.b
-        a = 2**(b - 2) + sum(2**i * ed25519raw.bit(h, i)
-                             for i in range(3, b - 2))
-        S = (r + ed25519raw.Hint(globalR + globalPk + digest) * a) % ed25519raw.l
+        a = 2**(b - 2) + sum(2**i * ed25519raw.bit(h, i) for i in range(3, b - 2))
+        S = (r + ed25519raw.Hint(global_R + global_pk + digest) * a) % ed25519raw.l
         print('Local sig %d: %s' % (i + 1, hex(ed25519raw.encodeint(S))))
-        commits.append(R)
         sigs.append(ed25519raw.encodeint(S))
 
     print('-----------------')
-    sig = combine_sig(globalR, [sigs[i] for i in keyset])
+    sig = combine_sig(global_R, [sigs[i] for i in keyset])
     print('Global sig: %s' % hex(sig))
-    ed25519raw.checkvalid(sig, digest, globalPk)
+    ed25519raw.checkvalid(sig, digest, global_pk)
     print('Valid Signature!')
 
 
diff --git a/tools/ed25519raw.py b/tools/ed25519raw.py
index 2fd060a9..24c7d687 100644
--- a/tools/ed25519raw.py
+++ b/tools/ed25519raw.py
@@ -14,7 +14,7 @@ def H(m):
 
 def expmod(b, e, m):
     if e < 0:
-        raise Exception("negative exponent")
+        raise Exception('negative exponent')
     if e == 0:
         return 1
     t = expmod(b, e >> 1, m)**2 % m
@@ -120,18 +120,18 @@ def decodepoint(s):
         x = q - x
     P = [x, y]
     if not isoncurve(P):
-        raise Exception("decoding point that is not on curve")
+        raise Exception('decoding point that is not on curve')
     return P
 
 
 def checkvalid(s, m, pk):
     if len(s) != b >> 2:
-        raise Exception("signature length is wrong")
+        raise Exception('signature length is wrong')
     if len(pk) != b >> 3:
-        raise Exception("public-key length is wrong")
+        raise Exception('public-key length is wrong')
     R = decodepoint(s[0:b >> 3])
     A = decodepoint(pk)
     S = decodeint(s[b >> 3:b >> 2])
     h = Hint(encodepoint(R) + pk + m)
     if scalarmult(B, S) != edwards(R, scalarmult(A, h)):
-        raise Exception("signature does not pass verification")
+        raise Exception('signature does not pass verification')