Kirk

From PSP Developer wiki
Jump to navigation Jump to search

The PSP KIRK Crypto Engine is a security hardware device that is embedded into the TACHYON main IC chip. It is a bus master and can DMA to/from main DDR RAM memory, operating independantly of the CPU. It is intefaced via memory mapped registers at base of 0xBDE00000 (SPOCK Crypto Engine on the other hand is mapped to 0xBDF00000). It is capable of performing AES encryption, decryption, SHA1 Hash, pseudo random number generation, and signature generation and verifications (ECDSA) and CMAC.

All (or almost all) the static keys used by the engine (plus the private key for KIRK CMD1) have been found through the PS3 hacks or glitching and can be found on the Keys page.

Invocation

All of the Kirk commands can be used using the function sceUtilsBufferCopyWithRange, which takes five arguments:

  • the output buffer (if there is one, NULL otherwise)
  • the output buffer size (if there is one, 0 otherwise)
  • the input buffer (if there is one, NULL otherwise)
  • the input buffer size (if there is one, 0 otherwise)
  • the index of the command (as detailed below).

Elliptic curves

The PSP uses ECDSA for public-key cryptography. Elliptic curves are known for being fast and only requiring small keys, contrary to other public-key cryptography algorithms. They are still considered to be very secure, even for the 160-bit curves used by the PSP, unless a mistake is made when using them.

These curves have been designed by Sony only for the console. They are not vulnerable to any known attack.

Both use the usual Weierstrass form.

Elliptic curve for CMD1

This curve is used for the ECDSA verification of CMD1. 

p = 0xFFFFFFFFFFFFFFFF0001B5C617F290EAE1DBAD8F
G = (0x2259ACEE15489CB096A882F0AE1CF9FD8EE5F8FA, 0x604358456D0A1CB2908DE90F27D75C82BEC108C0)
n = 0xFFFFFFFFFFFFFFFF00000001FFFFFFFFFFFFFFFF
a = -3
b = 0x65D1488C0359E234ADC95BD3908014BD91A525F9

The public key is hardcoded, and is equal to: (0xED9CE58234E61A53C685D64D51D0236BC3B5D4B9, 0x049DF1A075C0E04FB344858B61B79B69A63D2C39).

Elliptic curve for the other commands

This curved is used for Kirk commands 0xC, 0xD, 0x10, 0x11, and likely 0x12. 

p = 0xFFFFFFFFFFFFFFFEFFFFB5AE3C523E63944F2127
G = (0x128EC4256487FD8FDF64E2437BC0A1F6D5AFDE2C, 0x5958557EB1DB001260425524DBC379D5AC5F4ADF)
n = 0xFFFFFFFFFFFFFFFF00000001FFFFFFFFFFFFFFFF
a = -3
b = 0xA68BEDC33418029C1D3CE33B9A321FCCBB9E0F0B

The public key is variable. For the latest Pre-IPL version which add an additional ECDSA verification of the XOR of the block hashes, the public key is (0xBC660611A70BD7F2D140A48215C096D11D2D4112, 0xF0E9379AC4E0D387C542D091349DD15169DD5A87).

Code sample

Below is an example of how to manipulate these curves using the ecpy python library. 

import ecpy.curves

psp_curve_cmd1 = {
    'name':      "psp_curve_cmd1",
    'type':      "weierstrass",
    'size':      160,
    'field':     0xFFFFFFFFFFFFFFFF00000001FFFFFFFFFFFFFFFF,
    'generator': (0x2259ACEE15489CB096A882F0AE1CF9FD8EE5F8FA, 0x604358456D0A1CB2908DE90F27D75C82BEC108C0),
    'order':     0xFFFFFFFFFFFFFFFF0001B5C617F290EAE1DBAD8F,
    'cofactor':  1,
    'a':         -3,
    'b':         0x65D1488C0359E234ADC95BD3908014BD91A525F9,
}

psp_curve_cmd17 = {
    'name':      "psp_curve_cmd17",
    'type':      "weierstrass",
    'size':      160,
    'field':     0xFFFFFFFFFFFFFFFF00000001FFFFFFFFFFFFFFFF,
    'generator': (0x128EC4256487FD8FDF64E2437BC0A1F6D5AFDE2C, 0x5958557EB1DB001260425524DBC379D5AC5F4ADF),
    'order':     0xFFFFFFFFFFFFFFFEFFFFB5AE3C523E63944F2127,
    'cofactor':  1,
    'a':         -3,
    'b':         0xA68BEDC33418029C1D3CE33B9A321FCCBB9E0F0B,
}

crv1 = ecpy.curves.WeierstrassCurve(psp_curve_cmd1)
crv17 = ecpy.curves.WeierstrassCurve(psp_curve_cmd17)

pt1 = ecpy.curves.Point(0xED9CE58234E61A53C685D64D51D0236BC3B5D4B9, 0x049DF1A075C0E04FB344858B61B79B69A63D2C39, crv1)
pt17 = ecpy.curves.Point(0xbc660611a70bd7f2d140a48215c096d11d2d4112, 0xf0e9379ac4e0d387c542d091349dd15169dd5a87, crv17)

# verify the KIRK1 ECDSA private key
crv1_g = ecpy.curves.Point(0x2259ACEE15489CB096A882F0AE1CF9FD8EE5F8FA, 0x604358456D0A1CB2908DE90F27D75C82BEC108C0, crv1)
assert(crv1.mul_point(crv1.generator, 0xF392E26490B80FD889F2D9722C1F34D7274F983D) == pt1)

Commands

On PSP there are 18 KIRK commands. On PSVita, there are these 18 commands plus some new commands to support bigger keys (192 bits for example). See F00D commands.

KIRK functions are called with the same 5 arguments (outbuf, outbuf_size, inbuf, inbuf_size, service_number (which is the command ID)). Depending on the service number used, the expectations of the inbuf or outbuf vary and are detailed below.

Table

Command ID Name Short description Input size Output size Used in
1 KIRK_CMD_DECRYPT_PRIVATE Super-Duper decryption (no inverse) buf_size+0x90 buf_size memlmd, mesg_led
2 KIRK_CMD_DNAS_ENCRYPT Encrypt Operation for DNAS (inverse of cmd 3) buf_size+0x90 buf_size
3 KIRK_CMD_DNAS_DECRYPT Decrypt Operation for DNAS (inverse of cmd 2) buf_size+0x90 buf_size
4 KIRK_CMD_ENCRYPT_STATIC Encrypt Operation (inverse of cmd 7) (key=static) buf_size+0x14 buf_size+0x14 chnnlsv, memab
5 KIRK_CMD_ENCRYPT_PERCONSOLE Encrypt Operation (inverse of cmd 8) (key=per-console) buf_size+0x14 buf_size+0x14 chnnlsv, psheet since PSP FW 2.81 for PGD, ?openpsid for IDS Certificates?
6 KIRK_CMD_ENCRYPT_USER Encrypt Operation (inverse of cmd 9) (key=user-defined) ? ?
7 KIRK_CMD_DECRYPT_STATIC Decrypt Operation (inverse of cmd 4) (key=static) buf_size+0x14 buf_size+0x14 memlmd, mesg_led,chnnlsv, memab
8 KIRK_CMD_DECRYPT_PERCONSOLE Decrypt Operation (inverse of cmd 5) (key=per-console) buf_size+0x14 buf_size+0x14 chnnlsv, psheet since PSP FW 2.81 for PGD
9 KIRK_CMD_DECRYPT_USER Decrypt Operation (inverse of cmd 6) (key=user-defined) ? ?
10 (0xA) KIRK_CMD_PRIV_SIGVRY Private Signature Verify (checks for private SCE sig) buf_size+0x90 0
11 (0xB) KIRK_CMD_HASH SHA1 Hash buf_size >= 0x14 0x14 memlmd, mesg_led, memab
12 (0xC) KIRK_CMD_ECDSA_GENKEY ECDSA Generate Private/Public Key Pair 0 0x3C memab
13 (0xD) KIRK_CMD_ECDSA_MUL ECDSA Multiply Point 0x3C 0x3C
14 (0xE) KIRK_CMD_PRNGEN Pseudo Random Number Generation 0 0x14 mesg_led, chnnlsv, memab, semawm
15 (0xF) KIRK_CMD_15 (absolutely no idea – could be KIRK initialization or PRNG reseeding) 0 0 IPL
16 (0x10) KIRK_CMD_SIGGEN ECDSA Signature Generation 0x34 0x28 memab
17 (0x11) KIRK_CMD_SIGVRY Signature Verification (checks for generated signatures) 0x64 0 memab
18 (0x12) KIRK_CMD_CERTVRY Certificate Verification (IDStorage Certificates CMAC) 0xB8 0 openpsid, memab

Command 1: decryption and authentication

Overview

This function is used to both decrypt and verify the signature of the IPL blocks.

There are two versions of this service: AES CMAC Verification, and ECDSA Verification. They use the header section of the input buffer slightly differently.

In both cases, the total header length is 0x90. The first 0x60 bytes depend on the version. The last 0x30 bytes are the same in both cases:

Metadata Header Structure (Length 0x30):

Address Size Description
0x60 4 Set to 1
0x64 4 0 indicates AES CMAC version, 1 indicates ECDSA version
0x68 4 0
0x6C 4 0 for retail version and 0xFFFFFFFF for dev versions
0x70 4 Length of decrypted data
0x74 4 Length of the padding after the header and before the real data
0x78 8 0

AES CMAC Version

Key Header Structure (Length 0x60):

Address Size Description
0x00 16 Decryption key, encrypted with the KIRK1 AES master key
0x10 16 CMAC key, encrypted with the KIRK1 AES master key
0x20 16 Header hash (CMAC)
0x30 16 Data hash (CMAC)
0x40 32 0

Decryption process

The first 0x20 bytes of the Key Header are decrypted with the KIRK 1 Stored AES Key. This was allegedly discovered by Datel by decapping the chip and reversing engineering the algorithms and keys. This was also recovered through the failure in PS3 cryptography by decrypting the isolated module in the PSP emulator on the PS3.

The first block is the AES Key used for decrypting the main data. The second block is used to decrypt the next two blocks (0x20 bytes at offset 0x20). These represent the Metadata Header CMAC and the Data CMAC. They are checked against the AES CMAC of the metadata header section and the AES CMAC of the whole data, from the metadata header section to the end of the data (including padding in-between).

ECDSA Version

Key Header Structure (Length 0x60):

Address Size Description
0x00 0x10 Decryption key, encrypted with the KIRK1 AES master key
0x10 0x14 Header ECDSA signature r
0x24 0x14 Header ECDSA signature s
0x38 0x14 Data ECDSA signature r
0x4C 0x14 Data ECDSA signature s

Decryption process

The ECDSA version is slightly different. Only the first block (0x10 bytes) is decrypted with the Kirk 1 AES Key. It is used to decrypt the main data section just as in the AES CMAC version. Rather than a CMAC, the Metadata header is checked by SHA1 hashing its 0x30 bytes and checking the signature components through a ECDSA Verify call. The encrypted Data section is also checked via SHA1 of the entire data through a ECDSA Verify call.

The ECDSA curve parameters are indicated above.

Commands 2 & 3: DRM encrypt & decrypt

These commands are mostly unknown. The header is the same as KIRK command 1, with the mode set to 2 or 3.

In command 2, the input data passed to KIRK is first checked (presumably CMAC), then decrypted, and re-encrypted with the console unique private key. Having that common key would allow legit creation of DRM BB install packages.

Command 3 is the decryption counterpart of command 2.

Commands 4~9: AES encrypt & decrypt

All these commands do AES128-CBC encryption/decryption with an IV equal to 0. - Commands 4 (encryption) and 7 (decryption) use a one of the 128 keys stored in the Kirk chip and available on the Keys page, index being given by the keyseed field (which must be between 0x00 and 0x7F) - Commands 5 (encryption) and 8 (decryption) use an unknown per-console key (it is unknown if it is derived from other data, or just stored as-is on the chip) - Commands 6 (encryption) and 9 (decryption) use a key derived from the keyseed using an unknown key derivation function

In all cases, data is prefixed with a 0x14-byte long header:

Address Size Description
0x00 4 Mode: must be 4 for encryption, 5 for decryption
0x04 8 Unknown (0?)
0x0C 4 Keyseed
0x10 4 Size of the following data

Command 10: AES CMAC verification

This seems to be the AES CMAC verification of CMD1, and takes the same header as CMD1, the only difference is that no decryption is performed.

See command 1 information for details.

It could also possibly verify CMACs for commands 2 & 3, but that is unknown.

Command 11: SHA1

This command computes the SHA1 of the input. The input must be prefixed with a 4-byte header giving the length of the buffer. Output is 0x14-byte long.

Command 12: ECDSA key pair generation

This command generates a random private key and computes the associated public key. See above for the parameters of the elliptic curve.

This returns the following into the keypair buffer, of size 0x3C (each value is 0x14 bytes long):

  • 0x00 - randomly generated private key
  • 0x14 - Public Key point x value
  • 0x28 - Public Key point y value

Command 13: ECDSA point multiplication

This command multiplies an elliptic curve point by a scalar. See above for the parameters of the elliptic curve.

Input (size 0x3c):

  • 0x00 - scalar k
  • 0x14 - point x value P.x
  • 0x28 - point y value P.y

Output (size 0x28):

  • 0x00 - point x value (kP).x
  • 0x14 - point y value (kP).y

The result is a new point(x and y are each 0x14 bytes long).

Command 14: PRNG

This function takes no input and generates random data of the given size (depending on the specified size of the output buffer).

Command 15: init?

This function takes no input and no output.

It could be either a Kirk initialization, or a PRNG re-seeding.

Command 16: ECDSA signature generation

This command generates an ECDSA signature of a SHA1 hash (0x14 buffer) using an encrypted private key.

Input is:

  • 0x00: 0x20-byte long encrypted buffer containing the private key
  • 0x20: the message hash.

The output is a 0x28-byte long signature (r and s, both 0x14-byte long).

The private key buffer is encrypted with a device-specific encryption using the FuseID.

Here is the code of the decryption, thanks to Davee & Proxima. g_fuse90 and g_fuse94 are the two words composing the FuseID (present at the 0xBC100090 and 0xBC100094 hardware registers). Output is 0x20-byte long, but the last 0xC bytes are ignored (and possibly always equal to zero) for the private key. 

void decrypt_kirk16_private(u8 *dA_out, u8 *dA_enc)
{   
  int i, k;
  kirk16_data keydata;
  u8 subkey_1[0x10], subkey_2[0x10];
  rijndael_ctx aes_ctx;
  
  keydata.fuseid[7] = g_fuse90 &0xFF;
  keydata.fuseid[6] = (g_fuse90>>8) &0xFF;
  keydata.fuseid[5] = (g_fuse90>>16) &0xFF;
  keydata.fuseid[4] = (g_fuse90>>24) &0xFF;
  keydata.fuseid[3] = g_fuse94 &0xFF;
  keydata.fuseid[2] = (g_fuse94>>8) &0xFF;
  keydata.fuseid[1] = (g_fuse94>>16) &0xFF;
  keydata.fuseid[0] = (g_fuse94>>24) &0xFF;
 
  /* set encryption key */
  rijndael_set_key(&aes_ctx, kirk16_key, 128);
  
  /* set the subkeys */
  for (i = 0; i < 0x10; i++)
  {
    /* set to the fuseid */
    subkey_2[i] = subkey_1[i] = keydata.fuseid[i % 8];
  } 

  /* do aes crypto */
  for (i = 0; i < 3; i++)
  {
    /* encrypt + decrypt */
    rijndael_encrypt(&aes_ctx, subkey_1, subkey_1);
    rijndael_decrypt(&aes_ctx, subkey_2, subkey_2);
  }

  /* set new key */
  rijndael_set_key(&aes_ctx, subkey_1, 128);

  /* now lets make the key mesh */
  for (i = 0; i < 3; i++)
  {
    /* do encryption in group of 3 */
    for (k = 0; k < 3; k++)
    {
      /* crypto */
      rijndael_encrypt(&aes_ctx, subkey_2, subkey_2);
    }

    /* copy to out block */
    memcpy(&keydata.mesh[i * 0x10], subkey_2, 0x10);
  }

  /* set the key to the mesh */
  rijndael_set_key(&aes_ctx, &keydata.mesh[0x20], 128);

  /* do the encryption routines for the aes key */
  for (i = 0; i < 2; i++)
  {
    /* encrypt the data */
    rijndael_encrypt(&aes_ctx, &keydata.mesh[0x10], &keydata.mesh[0x10]);
  }

  /* set the key to that mesh shit */
  rijndael_set_key(&aes_ctx, &keydata.mesh[0x10], 128);

  /* cbc decrypt the dA */
  AES_cbc_decrypt((AES_ctx *)&aes_ctx, dA_enc, dA_out, 0x20);
}

Command 17: ECDSA signature verification

This command verifies an ECDSA signature using the ECDSA curve described above.

It takes no output, and takes as an input:

  • 0x00: public key
  • 0x28: signed message hash
  • 0x3C: signature r
  • 0x50: signature s

The result of the operation is given by the return value (0 on success, 5 on failure to verify the signature).

Command 18

Unknown.

Code Samples

Open problems

  • The private key corresponding to the latest version PRE-IPL public key is unknown.
  • Commands 2, 3, 5, 6, 8, 9 & 18 (and partly 10) are mostly unknown and need testing/documentation.
Retrieved from "http://www.psdevwiki.com/psp/index.php?title=Kirk&oldid=11565"