SELF - SPRX
SELF stands for Signed Executable and Linkable Format.
Introduction
It is the format used by the executables on the PS3 It has a specific header here called SCE header where it stores all the parameters for this process
- SCE Header
It consist on information regarding the structure and offsets of the self. The first part is in plaintext until you reach Metadata Info.
- Metadata Info
Metadata Info is itself under AES 256 CBC. This part contains KEY + IV to further decrypt the header using AES 128 CTR.
- Metadata
The metadata header, Metadata Section Headers, Section Hash, Capabilities and Signature are under this AES 128 CTR layer and is decrypted with the key above.
- Metadata Header
Metadata header contains the info required to authenticate the header and the structure of the metadata. The signature is ECDSA of the SHA1 hash of the self file starting at 0x0 and ending at 0x0+signatureInputLength
- Data Sections
The data sections might be encrypted using AES 128 CTR and/or compressed. HMAC-SHA1 is used to authenticate they have not been modified.
Note: not only ELF/PRX files can be signed with this format, other known files with SCE header are :
- revoke (e.g. RL_FOR_PACKAGE.img/RL_FOR_PROGRAM.img and pkg.srvk/prog.srvk)
- spp (e.g. default.spp)
- package (e.g. .pkg/.spkg_hdr.X)
- edat
Cryptography
Here is a small summary on how the self cryptography works.
Basically here are the steps being involved by the loaders:
Loaders all have a static key and iv called respectively erk and riv, those are keys for the first decryption step which are used to decrypt the very first 0x40 bytes of the self's metadata using AES256CBC
Then the result is used as a key and iv to decrypt the rest of the metadata using AESCTR, finally the decrypted metadata contains the keys and iv for each data sections which are still decrypted through AES128CTR. This security model is based on the fact that the first 0x40 bytes of the self's metadata once decrypted by the static AES256CBC key in the loader should never be the same from one binary to the other. The same goes for any other value used as an AES128CTR key or iv.
Loaders are also involved with inflating the binaries using zlib.
The self authenticity is based on other independent steps, HMAC-SHA1 and ECDSA for the actual signature.
Short references
More indepth Online course about encryption in generic (also AES/ECDSA): Lecture Notes on Computer and Network Security by Avinash Kak
File Format
Notes:
- Numbers are stored in big endian format.
SELF/SCE Header
Struct
typedef struct {
uint32_t magic; /* 53434500 = SCE\0 */
uint32_t hdr_version; /* header version */
uint16_t key_revision; /* 0x0 retail (type 0)
* 0x1 retail (0.92-3.30)
* 0x2 retail (type 1)
* 0x3 unknown (npdrm1?)
* 0x4 retail (3.40-3.42)
* 0x5 unknown (npdrm1?)
* 0x6 unknown (npdrm2?)
* 0x7 retail (3.50)
* 0x8 unknown (npdrm1?)
* 0x9 unknown (npdrm2?)
* 0xa retail (3.55)
* 0xb unknown (npdrm1?)
* 0xc unknown (npdrm2?)
* 0xd retail (3.56)
* 0xe unknown (npdrm1?)
* 0xf unknown (npdrm2?)
* 0x10 retail (3.60-3.61)
* 0x11 unknown (npdrm1?)
* 0x12 unknown (npdrm2?)
* 0x13 retail (3.65)
* 0x14 unknown (npdrm1?)
* 0x15 unknown (npdrm2?)
* 0x16 retail (3.70-3.74)
* 0x17 unknown (npdrm1?)
* 0x18 unknown (npdrm2?)
* 0x19 retail (4.00)
* 0x8000 DEBUG (devkit)
*/
uint16_t header_type; /* 1 self, 2 unknown, 3 pkg */
uint32_t metadata_offset; /* metadata offset */
uint64_t header_length; /* self header length */
uint64_t elf_length; /* ELF file length */
uint64_t unknown; /* UNKNOWN always 3 */ uint64_t appinfo_offset; /* app info offset */ uint64_t elf_offset; /* ELF #1 offset */ uint64_t phdr_offset; /* program header offset */ uint64_t shdr_offset; /* section header offset */ uint64_t section_info_offset; /* section info offset */ uint64_t sceversion_offset; /* version offset */ uint64_t controlinfo_offset; /* control info offset */ uint64_t controlinfo_length; /* control length */ uint64_t padding; /* padding */
} __attribute__((packed)) SELF;
Table
| field | offset | type | notes |
|---|---|---|---|
| sce_magic | 0x0 | u32 | Must be "SCE\0" |
| header_version | 0x4 | u32 | This must be 2 or the Self loader will abort |
| key_revision | 0x8 | u16 | This corresponds to the revision of the key to decrypt the metadata header, see: appldr, key structure in loaders
key_obj = key_table[sdk_type] |
| header_type | 0xA | u16 | 1 self, 2 rvk, 3 pkg, 4 spp |
| metadata_offset | 0xC | u32 | Offset to the checksums. Must be at least 20 bytes before the end of the header |
| header_length | 0x10 | u64 | This is the length of the header (including the fake elf headers)
|
| Encrypted size | 0x18 | u64 | The size of the encrypted part of the self file. |
| unknown | 0x20 | u64 | Must be 3, or 80010007 error |
| app_info_offset | 0x28 | u64 | An offset in the header, usually at 0x70. See App info header. |
| elf_offset | 0x30 | u64 | offset to the elf header |
| phdr_offset | 0x38 | u64 | offset to phdr |
| shdr_offset | 0x40 | u64 | offset to shdr |
| encrypted phdr sizes/offsets table offset | 0x48 | u64 | Offset to a table which maps phdr entries to the actual offset/size within the encrypted fself.
Because fselfs can be compressed, they might not match the values listed within the elf. |
| sceversion header | 0x50 | u64 | Offset to a header which contains some version information, including an offset to the .sceversion section of the encrypted elf.
The playstation 3 doesn't care about this, and doesn't even check the header |
| control info offset | 0x58 | u64 | |
| control info length | 0x60 | u64 | |
| padding | 0x68 | u64 |
comments
The real ELF data is located after the SCE header (see header size). It is encrypted, unless the flags are 0x8000. unfself works by cutting the SCE header from the (fake) SELF.
App Info
Struct
typedef struct {
uint64_t authid; /* auth id */
uint32_t vendor_id; /* vendor id */
uint32_t self_type; /* app type
* 1 level0,
* 2 level1,
* 3 level2,
* 4 application,
* 5 isolated SPU module,
* 6 secure loader,
* 7 unknown, handled by appldr,
* 8 NPDRM app */
uint64_t version; /* app version */
uint64_t padding; /* UNKNOWN */
} __attribute__((packed)) APP_INFO;
Table
| field | offset | type | notes |
|---|---|---|---|
| authid | 0x00 | u64 | |
| unknown | 0x08 | u32 | |
| app_type | 0x0c | u32 |
*1 -- level 0
*2 -- level 1
*3 -- level 2
*4 -- application
*5 -- isolated SPU module
*6 -- secure loader
*8 -- NP-DRM application
|
| app_version | 0x10 | u64 |
Comments
Aligned to 0x10 bytes.
ELF Header
Struct
typedef struct {
uint8_t e_ident[16]; /* ELF identification */
uint16_t e_type; /* object file type */
uint16_t e_machine; /* machine type */
uint32_t e_version; /* object file version */
uint64_t e_entry; /* entry point address */
uint64_t e_phoff; /* program header offset */
uint64_t e_shoff; /* section header offset */
uint16_t e_flags; /* processor-specific flags */
uint32_t e_ehsize; /* ELF header size */
uint16_t e_phentsize; /* size of program header entry */
uint16_t e_phnum; /* number of program header entries */
uint16_t e_shentsize; /* size of section header entry */
uint16_t e_shnum; /* number of section header entries */
uint16_t e_shstrndx; /* section name string table index */
} __attribute__((packed)) ELF;
Table
Comments
See Specifications here: ELF Header ELF-64 Object File Format
Notes:
- e_type: ET_PS3PRX=0xFFA4
- EI_OSABI: ELFOSABI_CELL_LV2=0x66
ELF Program Headers
Struct
typedef struct {
uint32_t p_type; /* type of segment */
uint32_t p_flags; /* segment attributes */
uint64_t p_offset; /* offset in file */
uint64_t p_vaddr; /* virtual address in memory */
uint64_t p_paddr; /* reserved */
uint64_t p_filesz; /* size of segment in file */
uint64_t p_memsz; /* size of segment in memory */
uint64_t p_align; /* alignment of segment */
} __attribute__((packed)) ELF_PHDR;
Table
Comments
See Spec here: ELF Program Headers
ELF Section Headers
Struct
typedef struct {
uint32_t sh_name; /* section name */
uint32_t sh_type; /* section type */
uint64_t sh_flags; /* section attributes */
uint64_t sh_addr; /* virtual address in memory */
uint64_t sh_offset; /* offset in file */
uint64_t sh_size; /* size of section */
uint32_t sh_link; /* link to other section */
uint32_t sh_info; /* miscellaneous information */
uint64_t sh_addralign; /* address alignment boundary */
uint64_t sh_entsize; /* size of entries, if section has table */
} __attribute__((packed)) ELF_SHDR;
Table
Comments
Segment Information
Struct
typedef struct {
uint64_t offset; uint64_t size; uint32_t compressed; // 2=compressed uint32_t unknown1; uint32_t unknown2; uint32_t encrypted; // 1=encrypted
} __attribute__((packed)) SECTION_INFO;
Table
| field | offset | type | notes |
|---|---|---|---|
| Encrypted Data Offset | 0x00 | u64 | |
| Encrypted Data Size | 0x08 | u64 | |
| unknown | 0x10 | u32 | This has been 1 in all the examples I have seen. |
| unknown | 0x14 | u32 | Always 0, as far as I know. |
| unknown | 0x18 | u32 | Always 0, as far as I know. |
| unknown | 0x1c | u32 | This is 2 for loadable segment types, and 0 for other types. |
Comments
There is one of these entries for each phdr entry in the elf file so that the ps3 knows where to decrypt the data from. (because it might also be compressed.)
Notes:
- There is one Segment Information for each ELF Program Header.
SCE Version Info
Struct
typedef struct {
uint32_t unknown1; uint32_t unknown2; uint32_t unknown3; uint32_t unknown4;
} __attribute__((packed)) SCEVERSION_INFO;
Table
Comment
Control Information
Struct
typedef struct {
uint32_t type; // 1==control flags; 2==file digest; 3==npdrm uint32_t size; uint64_t unknown; // 0;1
union {
// type 1 0x30 bytes
struct {
uint32_t ctrl_flag1; // 0x80000000(all?);0x40000000(root);0x20000000(dbg);0x00000000(normal?)
uint32_t unknown2;
uint32_t unknown3;
uint32_t unknown4;
uint32_t unknown5;
uint32_t unknown6;
uint32_t unknown7; // 0;8;9;0xC
uint32_t unknown8; // 0;1;2;4
} control_flags;
// type 2 0x40 bytes
struct {
uint8_t digest1[20]; //hash digest, same for every file
uint8_t digest2[20]; //sha1 hash digest calculated of .elf file...
uint64_t padding;
} file_digest40;
// type 2 0x30 bytes
struct {
uint8_t digest1[20];
uint64_t unknown2;
} file_digest30;
// type 3 0x90 bytes
struct {
uint32_t magic;
uint32_t unknown2;
uint32_t license; /* 1 network, 2 local, 3 free */
uint32_t type; /* 1 exec, 21 update */
uint8_t content_id[48];
uint8_t digest[16];
uint8_t invdigest[16];
uint8_t xordigest[16];
uint64_t unknown3;
uint64_t unknown4;
} npdrm;
};
} __attribute__((packed)) CONTROL_INFO;
Table
Comments
Metadata Information
Struct
typedef struct {
uint8_t key[16]; uint8_t key_pad[16]; uint8_t iv[16]; uint8_t iv_pad[16];
} __attribute__((packed)) METADATA_INFO;
Table
Comments
Notes:
- The key and ivec fields are encrypted using AES256CBC.
- This is not present if it is an FSELF.
Metadata Header
Struct
typedef struct {
uint64_t signatureInputLength; uint32_t unknown02; uint32_t sectionCount; uint32_t keyCount; uint32_t signatureInfoSize; uint32_t unknown06; uint32_t unknown07;
} __attribute__((packed)) METADATA_HEADER;
Table
Comments
Notes:
- The metadata header is located after the metadata info in the SELF file.
- It is decrypted using AES128CTR with the key and ivec entries from the metadata information.
- The signature input length is the number of bytes which are used to generate the SHA-1 which is used to generate the ECDSA signature. The length should be eveything from the beginning until the signature itself. The decrypted version of the input data is used.
- This is only present if the metadata Information is present.
Metadata Section Headers
Struct
typedef struct {
uint64_t data_offset; uint64_t data_size; uint32_t type; // 1 = shdr, 2 == phdr, 3 == unknown uint32_t program_idx; uint32_t unknown; uint32_t sha1_idx; uint32_t encrypted; // 3=yes; 1=no uint32_t key_idx; uint32_t iv_idx; uint32_t compressed; // 2=yes; 1=no
} __attribute__((packed)) METADATA_SECTION_HEADER;
Table
Comments
Notes:
- The metadata section headers are located after the metadata header in the SELF file.
- The number of sections is indicated by the sectionCount entry in the metadata header.
- They are decrypted using AES128CTR with the key and ivec entries from the metadata information.
- Section data is decrypted using AES128CTR with the key and ivec from the metadata keys specified by keyIndex and ivecIndex.
- Section data will also need to be uncompressed using zlib.
- The dataOffsets of the metadata section headers match in general the segment information dataOffsets.
- This is only present if the metadata header is present.
Section Hash
Struct
typedef struct {
uint8_t sha1[20]; uint8_t padding[12]; uint8_t hmac_key[64];
} __attribute__((packed)) SECTION_HASH;
Table
Comments
Notes:
- The metadata keys (section hash) are located after the metadata section headers in the SELF file.
- The number of keys is indicated by the keyCount entry in the metadata header.
- They are decrypted using AES128CTR with the key and ivec entries from the metadata information.
- If the sha1Index points to a key, then key[sha1Index] and key[sha1Index+1] form the 160-bit hash. key[sha1Index+2] to key[key[sha1Index+6] form the 512-bit key for the HMAC-SHA1. The HMAC-SHA1 is calculated on the decrypted data and before the decompression.
Capabilities Info
Struct
typedef struct {
uint32_t unknown1; uint32_t capabilities_size; uint64_t unknown2; uint64_t unknown3; uint64_t unknown4; uint64_t flags; uint32_t unknown6; uint32_t unknown7;
} __attribute__((packed)) CAPABILITIES_INFO;
Table
Comments
Signature
Struct
typedef struct {
uint8_t r[21]; uint8_t s[21]; uint8_t padding[6];
} __attribute__((packed)) SIGNATURE;
Table
Comments
Notes:
- The signature is located after the the signature information in the SELF file.
- It is even present if the signature information is not present.
- It is decrypted using AES128CTR with the key and ivec entries from the metadata information.
Self Section Info
Struct
typedef struct {
uint8_t *data; uint64_t size; uint64_t offset;
} SELF_SECTION;
Table
Comments
Extracting an ELF
ELF Header
Elf64_Ehdr elfHeader; fseek ( selfFile, fix64 ( selfHeader.elfHeaderOffset ), SEEK_SET ); fread ( &elfHeader, sizeof ( Elf64_Ehdr ), 1, selfFile ); fseek ( elfFile, 0, SEEK_SET ); fwrite ( &elfHeader, sizeof ( Elf64_Ehdr ), 1, elfFile );
Section Headers
Elf64_Shdr elfSectionHeaders[100]; fseek ( selfFile, fix64 ( selfHeader.elfSectionHeadersOffset ), SEEK_SET ); fread ( elfSectionHeaders, sizeof ( Elf64_Shdr ), fix16 ( elfHeader.e_shnum ), selfFile ); fseek ( elfFile, fix64 ( elfHeader.e_shoff ), SEEK_SET ); fwrite ( elfSectionHeaders, sizeof ( Elf64_Shdr ), fix16 ( elfHeader.e_shnum ), elfFile );
Section Data
Notes:
- Unknown, manually copying the data over works for now.
- There should be a section data offset somewhere.
Program Headers
Elf64_Phdr elfProgramHeaders[100]; fseek ( selfFile, fix64 ( selfHeader.elfProgramHeadersOffset ), SEEK_SET ); fread ( elfProgramHeaders, sizeof ( Elf64_Phdr ), fix16 ( elfHeader.e_phnum ), selfFile ); fseek ( elfFile, fix64 ( elfHeader.e_phoff ), SEEK_SET ); fwrite ( elfProgramHeaders, sizeof ( Elf64_Phdr ), fix16 ( elfHeader.e_phnum ), elfFile );
Program Data
Notes:
- Load the metadata information and decrypt the key and ivec entries using AES256CBC using erk and riv.
- Load the metadata header and decrypt it using AES128CTR with the key and ivec entries from the metadata information.
- Load sectionCount metadata section headers and decrypt them using AES128CTR with the key and ivec entries from the metadata information.
- Load keyCount metadata keys and decrypt them using AES128CTR with the key and ivec entries from the metadata information.
- For each metadata section:
- In the SELF file, fseek to dataOffset and read in dataSize bytes.
- Decrypt the data using AES128CTR with the key and ivec from the metadata keys specified by keyIndex and ivecIndex from the metadata section header.
- Uncompress the data using zlib.
- Write it to the ELF file as the program section specified by section Index in the metadata section header.
Meta Checksums
There are 3 checksums at the offset specified by meta_offset.
- The first is the sha1 checksum of the entire self file.
- The 2nd checksum is the inverse of the first checksum.
- The 3rd checksum is the first checksum XORed with 0xAAAAAA..AAAAAB
The PSJailbreak payload ignores the actual checksums, but checks that the 3rd checksum is the 2nd checksum XORed with 0xAAAAAA..AAAAAB
Source: http://ps3wiki.lan.st/index.php?title=SELF_File_Format_and_Decryption