Kirk

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.

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	Result	Used in
1	KIRK_CMD_DECRYPT_PRIVATE	Super-Duper decryption (no inverse)	buf_size+0x40	buf_size		memlmd, mesg_led
2	KIRK_CMD_2	Encrypt Operation (inverse of cmd 3)
3	KIRK_CMD_3	Decrypt Operation (inverse of cmd 2)
4	KIRK_CMD_ENCRYPT_IV_0	Encrypt Operation (inverse of cmd 7) (IV=0)	buf_size+0x14	buf_size+0x14		chnnlsv, memab
5	KIRK_CMD_ENCRYPT_IV_FUSE	Encrypt Operation (inverse of cmd 8) (IV=FuseID)	buf_size+0x14	buf_size+0x14		chnnlsv, psheet since PSP FW 2.81 for PGD, ?openpsid for IDS Certificates?
6	KIRK_CMD_ENCRYPT_IV_USER	Encrypt Operation (inverse of cmd 9) (IV=UserDefined)
7	KIRK_CMD_DECRYPT_IV_0	Decrypt Operation (inverse of cmd 4) (IV=0)	buf_size+0x14	buf_size+0x14		memlmd, mesg_led,chnnlsv, memab
8	KIRK_CMD_DECRYPT_IV_FUSE	Decrypt Operation (inverse of cmd 5) (IV=FuseID)	buf_size+0x14	buf_size+0x14		chnnlsv, psheet since PSP FW 2.81 for PGD
9	KIRK_CMD_DECRYPT_IV_USER	Decrypt Operation (inverse of cmd 6) (IV=UserDefined)
10 (0xA)	KIRK_CMD_PRIV_SIGVRY	Private Signature Verify (checks for private SCE sig)
11 (0xB)	KIRK_CMD_HASH	SHA1 Hash	buf_size >= 0x14	?0x14?		memlmd, mesg_led, memab
12 (0xC)	KIRK_CMD_MUL1	ECDSA Generate Keys	0	0x3C		memab
13 (0xD)	KIRK_CMD_MUL2	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)				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 header section and the AES CMAC of the data section.

ECDSA Version

Key Header Structure (Length 0x60):

Address	Size	Description
0x00	16	Decryption key, encrypted with the KIRK1 AES master key
0x10	16	Header ECDSA signature r
0x24	16	Header ECDSA signature s
0x38	16	Data ECDSA signature r
0x4C	16	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 Data section is also checked via SHA1 of the entire data through a ECDSA Verify call.

The ECDSA curve parameters used for this ECDSA Verification are as follows.

p=FFFFFFFFFFFFFFFF00000001FFFFFFFFFFFFFFFF

NP=FFFFFFFFFFFFFFFF0001B5C617F290EAE1DBAD8F

a=-3

b=65D1488C0359E234ADC95BD3908014BD91A525F9

Base Point: Gx=2259ACEE15489CB096A882F0AE1CF9FD8EE5F8FA Gy=604358456D0A1CB2908DE90F27D75C82BEC108C0

Public Point: Px=ED9CE58234E61A53C685D64D51D0236BC3B5D4B9 Py=049DF1A075C0E04FB344858B61B79B69A63D2C39

Command 2 (DRM encrypt)

This command is mostly unknown. 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 12: ECDSA key pair generation

Elliptic Curve Math formula : <math>y^2 = x^3 +ax +b mod p</math> with NP points on the curve

p = FFFFFFFFFFFFFFFF00000001FFFFFFFFFFFFFFFF

N= FFFFFFFFFFFFFFFEFFFFB5AE3C523E63944F2127

a= -3

b= A68BEDC33418029C1D3CE33B9A321FCCBB9E0F0B

Base Point:

Gx= 128EC4256487FD8FDF64E2437BC0A1F6D5AFDE2C

Gy= 5958557EB1DB001260425524DBC379D5AC5F4ADF

Invocation:

u8 keypair[0x3c]
sceUtilsBufferCopyWithRange(keypair,0x3c,0,0,0xC);

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

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

Basically function 0xC generates a random number < N and multiplies it to the base point G to get the new public key.

Command 13: point multiplication

Elliptic Curve Math formula : <math>y^2 = x^3 +ax +b mod p</math> with NP points on the curve

p = FFFFFFFFFFFFFFFF00000001FFFFFFFFFFFFFFFF

NP= FFFFFFFFFFFFFFFEFFFFB5AE3C523E63944F2127

a= -3

b= A68BEDC33418029C1D3CE33B9A321FCCBB9E0F0B

Base Point:

Gx= 128EC4256487FD8FDF64E2437BC0A1F6D5AFDE2C

Gy= 5958557EB1DB001260425524DBC379D5AC5F4ADF

Invocation:

u8 buffer[0x3C]
u8 newpoint[0x28]
memcpy(buffer, multiplier, 0x14);
memcpy(buffer+0x14, pointx, 0x14);
memcpy(buffer+0x28, pointy, 0x14);
sceUtilsBufferCopyWithRange(newpoint,0x28,buffer,0x3c,0xD);

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

To test this, you can call 0xC service and copy the first 0x14 bytes to a new buffer, then copy the Gx and Gy values after that. Calling 0xD with the new buffer will return the values of x and y that were generated by the 0xC call.

Library

Calling commands using KIRK registers

• [1]

• [2]

• [3]

• [4]

Notes

In 2008 SilverSpring wrote:

Currently what is known about the cipher is that it is:
a block cipher operating in CBC mode
an all zero 128-bit initialization vector
128-bit block and key sizes
cmd4/7 uses a static key that is identical in all PSP’s
cmd5/8 uses a key based off the fuseID making all operations unique per PSP
cmd6/9 uses a user-defined 128-bit key
cmd1/2/3 uses the block cipher but also signature algorithms
the remaining KIRK cmd’s do not use the block cipher (sig, hash, & prng algo’s)