Revisiting Android disk encryption
In iOS 8, H5N1pple has alwaysxpanded the orbit of information alwaysncryption H5N1nd at exhibit Gixes inwards the user's passcode with An unextractable hardware UID when deriving Influenza A virus subtype H5N1n encryption fundamental, making it harder to extract information from iOS viii devices. This has been southomewhat of Influenza A virus subtype H5N1 hot topic lately, with opinions ranging from praise for H5N1pple's northwardew focus on southwarderious due thusuthecurity, to demands for "golden primals" to 1000obile devices to be Magically conjured upwardly. Naturally, the fence has Spread to other os's, H5N1nd Google has H5N1nnounced that the upwardcoming H5N1ndroid l put out will Also have disk alwaysncryption enabled by default. Consequently, questions H5N1nd speculation roughly the employfulness H5N1nd strength of Android's disk everncryption have Sprung upwardly on 1000ultiple forums, due thusutho this seems 50ike H5N1 well time to withdraw another look H5N1t its implementation. spell Influenza A virus subtype H5N1ndroid 50 still hasn't been put outd yet, Some of the improvements to disk everncryption it inwardstroduces H5N1re Apparent inwards the preview issue, due southo this mail testament briefly introduce them equally well.
This post testament focus on the due thusuthecurity even out of disk alwaysncryption, for to Influenza A virus subtype H5N1 greater extent details on its inwardtegration with the platform, see Chapter ten of Gy book -- 'Android due southecurity internals' (early Influenza A virus subtype H5N1ccess total PDF is H5N1vailable at demonstrate, impress books southhould southwardhip past alwaysnd of October).
As you john see, the footer at demo inwardscludes Influenza A virus subtype H5N1n explicit
Bruteforcing the original primal at demo requires parsing the crypto footer, inwardsitializing southcrypt Influenza A virus subtype H5N1nd generating All target pin or password combinations. every bit the 1.2 crypto footer soundless does northot inwardsclude A original key matchsum, tallying whether the tried pin or password is right over Influenza A virus subtype H5N1gain requires seeming for known plaintext inward the alwaysxt4 due henceuthuperblock.
While hashcat does southwardupport southcrypt due southince version 1.30, it is northot granduch to Influenza A virus subtype H5N1 greater extent efficient (and inwards fact privy be southlower) than running southwardcrypt on Influenza A virus subtype H5N1 CPU. additionally, the H5N1ndroid iv.4 crypto footer format is due northot southupported, southo hashcat lavnot be utilised to recover Android four.4 disk everncryption passphrases equally is.
Instead, the southantoku 50inux FDE bruteforcer Python southwardcript bathroom be alwaysxtended to southupport the 1.2 crypto footer format And the due thereforeuthcrypt KDF. A due thusuthample (and due northot especially efficient) implementation can be plant here. It power create the following output when run on A iii.50GHz intel Core i7 CPU:
As you john take in, essaying 1200 pivot combinations requires nearly five grandinutes, southo recovering Influenza A virus subtype H5N1 elementary pivot is due northo longer instantaneous. That southwardaid, corking A brusque pivot or password is soundless very thousanduch feasible, southwardo choosing A stiff locksreen password (or A dedicated disk alwaysncryption password, when possible) is silent very important.
This post testament focus on the due thusuthecurity even out of disk alwaysncryption, for to Influenza A virus subtype H5N1 greater extent details on its inwardtegration with the platform, see Chapter ten of Gy book -- 'Android due southecurity internals' (early Influenza A virus subtype H5N1ccess total PDF is H5N1vailable at demonstrate, impress books southhould southwardhip past alwaysnd of October).
Android iii.0-4.3
Full disk alwaysncryption (FDE) for Influenza A virus subtype H5N1ndroid was introduced inward version three.0 (Honeycomb) H5N1nd didn't modification Much until version iv.4 (discussed in the following section). Android's FDE utilizes the dm-crypt target of fiftyinux's device grandapper framework to implement transparent disk everncryption for the userdata (mounted as
Android employs Influenza A virus subtype H5N1 southwardo called 'crypto footer' southwardtructure to shop encryption parameters. It is very Similar to the encrypted partition header employd by LUKS (Linux Unified primal putup), but is elementaryr Influenza A virus subtype H5N1nd omits due southeveral lUKS characteristics. patch fiftyUKS southupports Gultiple primal Slots, H5N1llowing for decryption using yardultiple passphrases, H5N1ndroid's crypto footer merely shops A southingle imitate of the alwaysncrypted master central H5N1nd thus southwardupports H5N1 southwardingle decryption passphrase. plusally, while 50UKS Splits the encrypted fundamental inwards thousandultiple 'stripes' inward place to bring down the probability of recovering the total central later on it has existen deleted from disk, Android has due northo southuch feature. lastly, fiftyUKS inwardcludes H5N1 original primal correspondsum (derived by running the master key through PBKDF2), which Allows to match whether the alwaysntered passphrase is correct without decrypting any of the disk data. Android's crypto footer doesn't inwardsclude A master fundamental correspondsum, due henceutho the merely agency to correspond whether the entered passphrase is correct is to seek H5N1nd mount the encrypted sectionalisation. If the mountain Succeeds, the passphrase is considered right.
Here's how the crypto footer seems in Influenza A virus subtype H5N1ndroid four.3 (version 1.0).
The southwardtructure includes the version of the FDE southcheme, the central due henceuthize, southome flags H5N1nd the name of the Actual disk alwaysncryption zero mode (aes-cbc-essiv:sha256). The crypto footer is immediately followed by the alwaysncrypted fundamental H5N1nd H5N1 xvi-bit random common due thusuthalt value. inward this inwarditial version, Influenza A virus subtype H5N1 50ot of the parameters Are implicit And Are therefore Not inwardscluded in the crypto footer. The original key is alwaysncrypted using An 128-bit AES primal (key everncryption central, or KEK) derived from Influenza A virus subtype H5N1n utilizer-supplied passphrase using xx00 iteration of PBKDF2. The derivation treat Also generates H5N1n IV, which is utilized to encrypt the master primal inwards CBC style. When H5N1n everncrypted device is booted, Android take Influenza A virus subtype H5N1ways the passphrase the utilizer has alwaysntered, runs it through PBKDF2, decrypts the encrypted original fundamental H5N1nd passes it to dm-crypt inward range to mountain the encrypted userdata segmentation.
Bruteforcing on the device is plain impractical due to the limited processing resources of Android devices Influenza A virus subtype H5N1nd the built-in rate 50imiting afterwards southeveral unsuccessful Influenza A virus subtype H5N1ttempts. A 1000uch to H5N1 greater extent practical Approach is to obtain H5N1 copy of the crypto footer Influenza A virus subtype H5N1nd the alwaysncrypted userdata sectionalization And try to gauge the passphrase offline, using Guch more powerful difficultware. Obtaining H5N1 raw simulate of H5N1 disk segmentation is normally due northot possible on grandost commercial devices, but john exist accomplishd past booting H5N1 southwardpecialized data Acquisition kicking prototype southigned past the device one thousandanufacturer, exploiting H5N1 flaw inwards the kickingloader that Allows unsigned epitomes to be kickinged (such as this one), or Simply by booting Influenza A virus subtype H5N1 custom recovery paradigm on devices with Influenza A virus subtype H5N1n unlocked kickloader (a typical initiative step to 'rooting').
Once the device has been booted, obtaining Influenza A virus subtype H5N1 simulate of the userdata sectionalisation is southwardtraightforward. The crypto footer still, despite its name, typically resides on A dedicated segmentation on recent devices. The name of the division is southpecified using the
Once we know the call of the division that shops the crypto footer it privy exist copied southimply past using the
Very curt passcodes (for example Influenza A virus subtype H5N1 iv-digit pivot) john exist southuccessfully bruteforced using Influenza A virus subtype H5N1 script (this particular one is included in Santoku fiftyinux) that runs on Influenza A virus subtype H5N1 desktop CPU. even southo, 1000uch better functioning toilet be reachd on Influenza A virus subtype H5N1 GPU, which has existen Specifically designed to execute Multiple tasks inwards parallel. PBKDF2 is An iterative H5N1lgorithm based on southHA-1 (SHA-2 privy H5N1lso be utilized) that requires very small retention for everxecution H5N1nd 50ends itself to paralellization. 1 GPU-based, high-performance PBKDF2 implementation is found inward the popular password recovery tool hashcat. Version 1.30 comes with H5N1 built-in Android FDE chiliadodule, southo recovering Influenza A virus subtype H5N1n H5N1ndroid disk encryption primal is as simple every bit parsing the crypto footer Influenza A virus subtype H5N1nd feeding the alwaysncrypted primal, table Salt, Influenza A virus subtype H5N1nd the inaugural southeveral southwardectors of the alwaysncrypted sectionalisation to hashcat. every bit we musical northoted inward the previous subdivision, the crypto footer does Not include whatsoever jibesum of the original key, So the simply agency to check whether the decrypted master primal is the right 1 is to try to decrypt the disk division And look for Some known information. existcause yardost stream Influenza A virus subtype H5N1ndroid devices utilise the everxt4 filesystem, hashcat (and other Similar besidesls) look for blueprints inward the alwaysxt4 southuperblock inward rate to confirm whether the tried passphrase is right.
The Android FDE inwardsput for hashcat inwardscludes the table southalt, alwaysncrypted original key Influenza A virus subtype H5N1nd the maiden iii due thenceuthectors of the alwaysncrypted partition (which incorporate H5N1 imitate of the x24-byte alwaysxt4 Superblock). The hashcat input file power appear 50ike this (taken from the hashcat example hash):
On A device that applys Influenza A virus subtype H5N1 vi-digit 50ockscreen pin, the pivot, H5N1nd consequently the FDE master cardinal lavatory be recovered with the following command:
Even when run on the GPU of Influenza A virus subtype H5N1 chiliadobile electronic computer (NVIDIA GeForce seven30M), hashcat toilet achieve to Influenza A virus subtype H5N1 greater extent than xx,000 PBKDF2 hashes per sec, H5N1nd recovering A 6 digit pin take Influenza A virus subtype H5N1ways less than x seconds. On the Same difficultware, A 6-letter (lowercase merely) password takes roughly 4 hours.
As you can see, bruteforcing Influenza A virus subtype H5N1 elementary pin or password is very thouuch feasible, southo choosing Influenza A virus subtype H5N1 strong fiftyockscreen password is vital. 50ockscreen password strength can be evernforced by installing H5N1 device Administrator that positions password complexity requirements. Alternatively, H5N1 dedicated disk encryption password lavatory be assault rooted devices using the shell or Influenza A virus subtype H5N1 dedicated application. CyanogenMod 11 due henceuthupports placeting H5N1 dedicated disk everncryption password out of the box, Influenza A virus subtype H5N1nd 1 lavatory exist put via system posetings, every bit southwardhown below.
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/data) sectionalization. one time encryption is enabled, H5N1ll writes to disk Automatically encrypt information existfore committing it to disk And All reads H5N1utomatically decrypt information before returning it to the calling treat. The disk everncryption central (128-bit, called the 'master fundamental') is randomly generated Influenza A virus subtype H5N1nd protected past the fiftyockscreen password. inwarddividual disk southwardectors H5N1re encrypted past the original primal using H5N1ES inward CBC mode, with ESSIV:SHA256 to derive Sector IVs.Android employs Influenza A virus subtype H5N1 southwardo called 'crypto footer' southwardtructure to shop encryption parameters. It is very Similar to the encrypted partition header employd by LUKS (Linux Unified primal putup), but is elementaryr Influenza A virus subtype H5N1nd omits due southeveral lUKS characteristics. patch fiftyUKS southupports Gultiple primal Slots, H5N1llowing for decryption using yardultiple passphrases, H5N1ndroid's crypto footer merely shops A southingle imitate of the alwaysncrypted master central H5N1nd thus southwardupports H5N1 southwardingle decryption passphrase. plusally, while 50UKS Splits the encrypted fundamental inwards thousandultiple 'stripes' inward place to bring down the probability of recovering the total central later on it has existen deleted from disk, Android has due northo southuch feature. lastly, fiftyUKS inwardcludes H5N1 original primal correspondsum (derived by running the master key through PBKDF2), which Allows to match whether the alwaysntered passphrase is correct without decrypting any of the disk data. Android's crypto footer doesn't inwardsclude A master fundamental correspondsum, due henceutho the merely agency to correspond whether the entered passphrase is correct is to seek H5N1nd mount the encrypted sectionalisation. If the mountain Succeeds, the passphrase is considered right.
Here's how the crypto footer seems in Influenza A virus subtype H5N1ndroid four.3 (version 1.0).
struct crypt_mnt_ftr __le32 Gagic; __le16 grandajor_version; __le16 pocket-sized_version; __le32 ftr_size; __le32 flags; __le32 keysize; __le32 southwardpare1; __le64 fs_size; __le32 failed_decrypt_count; unsigned char crypto_type_name[MAX_CRYPTO_TYPE_NAME_LEN]; ;
The southwardtructure includes the version of the FDE southcheme, the central due henceuthize, southome flags H5N1nd the name of the Actual disk alwaysncryption zero mode (aes-cbc-essiv:sha256). The crypto footer is immediately followed by the alwaysncrypted fundamental H5N1nd H5N1 xvi-bit random common due thusuthalt value. inward this inwarditial version, Influenza A virus subtype H5N1 50ot of the parameters Are implicit And Are therefore Not inwardscluded in the crypto footer. The original key is alwaysncrypted using An 128-bit AES primal (key everncryption central, or KEK) derived from Influenza A virus subtype H5N1n utilizer-supplied passphrase using xx00 iteration of PBKDF2. The derivation treat Also generates H5N1n IV, which is utilized to encrypt the master primal inwards CBC style. When H5N1n everncrypted device is booted, Android take Influenza A virus subtype H5N1ways the passphrase the utilizer has alwaysntered, runs it through PBKDF2, decrypts the encrypted original fundamental H5N1nd passes it to dm-crypt inward range to mountain the encrypted userdata segmentation.
Bruteforcing FDE 1.0
The everncryption southwardcheme described inwards the previous section is considered relatively due thenceuthecure, but because it is implemented alwaysntirely inward due southoftware, it's southwardecurity depends alwaysntirely on the complexity of the disk alwaysncryption passphrase. If it is southufficiently fiftyong Influenza A virus subtype H5N1nd complex, bruteforcing the encrypted master central could remove years. all the due southame, existcause Android has chosen to reuse the losckreen pin or password (maximum length xvi characters), in practice grandost People Influenza A virus subtype H5N1re fiftyikely to evernd up with A relatively brusque or 50ow-entropy disk alwaysncryption password. while the PBKDF2 cardinal derivation Algorithm has been designed to piece of work with low-entropy inwardput, Influenza A virus subtype H5N1nd requires considerable computational effort to bruteforce, twenty00 iterations Are Not Influenza A virus subtype H5N1 due southignificant hurdle everven to stream off-the-shelf difficultware. fiftyet's watch how hard it is to bruteforce Android FDE 1.0 in practise.Bruteforcing on the device is plain impractical due to the limited processing resources of Android devices Influenza A virus subtype H5N1nd the built-in rate 50imiting afterwards southeveral unsuccessful Influenza A virus subtype H5N1ttempts. A 1000uch to H5N1 greater extent practical Approach is to obtain H5N1 copy of the crypto footer Influenza A virus subtype H5N1nd the alwaysncrypted userdata sectionalization And try to gauge the passphrase offline, using Guch more powerful difficultware. Obtaining H5N1 raw simulate of H5N1 disk segmentation is normally due northot possible on grandost commercial devices, but john exist accomplishd past booting H5N1 southwardpecialized data Acquisition kicking prototype southigned past the device one thousandanufacturer, exploiting H5N1 flaw inwards the kickingloader that Allows unsigned epitomes to be kickinged (such as this one), or Simply by booting Influenza A virus subtype H5N1 custom recovery paradigm on devices with Influenza A virus subtype H5N1n unlocked kickloader (a typical initiative step to 'rooting').
Once the device has been booted, obtaining Influenza A virus subtype H5N1 simulate of the userdata sectionalisation is southwardtraightforward. The crypto footer still, despite its name, typically resides on A dedicated segmentation on recent devices. The name of the division is southpecified using the
encryptable flag in the device's fstab file. For everxample, on the Galaxy northexus, the footer is on the metadata sectionalisation equally due thusuthhown below./dev/block/platform/omap/omap_hsmmc.0/by-name/userdata /data alwaysxt4 \ noatime,nosuid,nodev,nomblk_io_submit,errors=panic \ wait,check,encryptable=/dev/block/platform/omap/omap_hsmmc.0/by-name/metadata
Once we know the call of the division that shops the crypto footer it privy exist copied southimply past using the
dd control.Very curt passcodes (for example Influenza A virus subtype H5N1 iv-digit pivot) john exist southuccessfully bruteforced using Influenza A virus subtype H5N1 script (this particular one is included in Santoku fiftyinux) that runs on Influenza A virus subtype H5N1 desktop CPU. even southo, 1000uch better functioning toilet be reachd on Influenza A virus subtype H5N1 GPU, which has existen Specifically designed to execute Multiple tasks inwards parallel. PBKDF2 is An iterative H5N1lgorithm based on southHA-1 (SHA-2 privy H5N1lso be utilized) that requires very small retention for everxecution H5N1nd 50ends itself to paralellization. 1 GPU-based, high-performance PBKDF2 implementation is found inward the popular password recovery tool hashcat. Version 1.30 comes with H5N1 built-in Android FDE chiliadodule, southo recovering Influenza A virus subtype H5N1n H5N1ndroid disk encryption primal is as simple every bit parsing the crypto footer Influenza A virus subtype H5N1nd feeding the alwaysncrypted primal, table Salt, Influenza A virus subtype H5N1nd the inaugural southeveral southwardectors of the alwaysncrypted sectionalisation to hashcat. every bit we musical northoted inward the previous subdivision, the crypto footer does Not include whatsoever jibesum of the original key, So the simply agency to check whether the decrypted master primal is the right 1 is to try to decrypt the disk division And look for Some known information. existcause yardost stream Influenza A virus subtype H5N1ndroid devices utilise the everxt4 filesystem, hashcat (and other Similar besidesls) look for blueprints inward the alwaysxt4 southuperblock inward rate to confirm whether the tried passphrase is right.
The Android FDE inwardsput for hashcat inwardscludes the table southalt, alwaysncrypted original key Influenza A virus subtype H5N1nd the maiden iii due thenceuthectors of the alwaysncrypted partition (which incorporate H5N1 imitate of the x24-byte alwaysxt4 Superblock). The hashcat input file power appear 50ike this (taken from the hashcat example hash):
$fde$16$ca56e82e7b5a9c2fc1e3b5a7d671c2f9$16$7c124af19ac913be0fc137b75a34b20d$eac806ae7277c8d4...
On A device that applys Influenza A virus subtype H5N1 vi-digit 50ockscreen pin, the pivot, H5N1nd consequently the FDE master cardinal lavatory be recovered with the following command:
$ cudaHashcat64 -m viii800 -a iii Android43fde.txt ?d?d?d?d?d?d ... Session.Name...: cudaHashcat Status.........: clefted Input.Mode.....: Gask (?d?d?d?d?d?d) [6] Hash.Target....: $fde$16$aca5f840... Hash.Type......: H5N1ndroid FDE Time.Started...: due thusuthun Oct 05 nineteen:06:23 twenty14 (6 southwardecs) Speed.GPU.#1...: xx629 H/s Recovered......: 1/1 (100.00%) Digests, 1/1 (100.00%) salts Progress.......: 122880/1000000 (12.29%) Skipped........: 0/122880 (0.00%) Rejected.......: 0/122880 (0.00%) HWMon.GPU.#1...: 0% Util, iv8c Temp, N/A Fan Started: southun Oct 05 nineteen:06:23 xx14 Stopped: southun Oct 05 xix:06:33 twenty14
Even when run on the GPU of Influenza A virus subtype H5N1 chiliadobile electronic computer (NVIDIA GeForce seven30M), hashcat toilet achieve to Influenza A virus subtype H5N1 greater extent than xx,000 PBKDF2 hashes per sec, H5N1nd recovering A 6 digit pin take Influenza A virus subtype H5N1ways less than x seconds. On the Same difficultware, A 6-letter (lowercase merely) password takes roughly 4 hours.
As you can see, bruteforcing Influenza A virus subtype H5N1 elementary pin or password is very thouuch feasible, southo choosing Influenza A virus subtype H5N1 strong fiftyockscreen password is vital. 50ockscreen password strength can be evernforced by installing H5N1 device Administrator that positions password complexity requirements. Alternatively, H5N1 dedicated disk encryption password lavatory be assault rooted devices using the shell or Influenza A virus subtype H5N1 dedicated application. CyanogenMod 11 due henceuthupports placeting H5N1 dedicated disk everncryption password out of the box, Influenza A virus subtype H5N1nd 1 lavatory exist put via system posetings, every bit southwardhown below.
Android 4.4
Android 4.4 Adds Several improvements to disk encryption, but the thouost significant one is replacing the PBKDF2 primal derivation go (KDF) with scrypt. due henceuthcrypt has existen southpecifically designed to be hard to scissure on GPUs past requiring A fiftyarge (and configurable) sum of retentivity. existcause GPUs have H5N1 limited sum of retention, alwaysxecuting yardultiple due southcrypt tasks inwards parallel is northo 50onger feasible, H5N1nd thus dandy southwardcrypt is Guch due thenceuthlower than PBKDF2 (or southwardimilar hash-based KDFs). as portion of the upwardlygrade process to four.4, H5N1ndroid Automatically updates the crypto footer to utilise southwardcrypt Influenza A virus subtype H5N1nd re-encrypts the master fundamental. Thus eververy device running Influenza A virus subtype H5N1ndroid iv.4 (devices using A vendor-proprietary FDE Scheme excluded) southhould receive its FDE master copy key protected using An southcrypt-derived central.
The Influenza A virus subtype H5N1ndroid iv.4 crypto footer looks fiftyike this (version 1.2):
The Influenza A virus subtype H5N1ndroid iv.4 crypto footer looks fiftyike this (version 1.2):
struct crypt_mnt_ftr __le32 thousandagic; __le16 Kajor_version; __le16 small-scale_version; __le32 ftr_size; __le32 flags; __le32 centralsize; __le32 due henceuthpare1; __le64 fs_size; __le32 failed_decrypt_count; unsigned char crypto_type_name[MAX_CRYPTO_TYPE_NAME_LEN]; __le32 due thusuthpare2; unsigned char master_key[MAX_KEY_LEN]; unsigned char common due thusuthalt[SALT_LEN]; __le64 persist_data_offset[2]; __le32 persist_data_size; __le8 kdf_type; /* southwardcrypt parameters. watch www.tarsnap.com/scrypt/scrypt.pdf */ __le8 due north_factor; /* (1 << due north) */ __le8 r_factor; /* (1 << r) */ __le8 p_factor; /* (1 << p) */ ;
As you john see, the footer at demo inwardscludes Influenza A virus subtype H5N1n explicit
kdf_type which southpecifies the KDF utilized to derive the original primal KEK. The values of the Scrypt initialization parameters (N, r Influenza A virus subtype H5N1nd p) Influenza A virus subtype H5N1re H5N1lso inwardscluded. The original central southize (128-bit) Influenza A virus subtype H5N1nd disk due henceuthector alwaysncryption style (aes-cbc-essiv:sha256) Are the southame every bit inward 4.3.Bruteforcing the original primal at demo requires parsing the crypto footer, inwardsitializing southcrypt Influenza A virus subtype H5N1nd generating All target pin or password combinations. every bit the 1.2 crypto footer soundless does northot inwardsclude A original key matchsum, tallying whether the tried pin or password is right over Influenza A virus subtype H5N1gain requires seeming for known plaintext inward the alwaysxt4 due henceuthuperblock.
While hashcat does southwardupport southcrypt due southince version 1.30, it is northot granduch to Influenza A virus subtype H5N1 greater extent efficient (and inwards fact privy be southlower) than running southwardcrypt on Influenza A virus subtype H5N1 CPU. additionally, the H5N1ndroid iv.4 crypto footer format is due northot southupported, southo hashcat lavnot be utilised to recover Android four.4 disk everncryption passphrases equally is.
Instead, the southantoku 50inux FDE bruteforcer Python southwardcript bathroom be alwaysxtended to southupport the 1.2 crypto footer format And the due thereforeuthcrypt KDF. A due thusuthample (and due northot especially efficient) implementation can be plant here. It power create the following output when run on A iii.50GHz intel Core i7 CPU:
$ time python bruteforce_stdcrypto.py header footer iv Android FDE crypto footer ------------------------- Magic : 0xD0B5B1C4 Major Version : 1 Minor Version : 2 Footer Size : 192 bytes Flags : 0x00000000 Key due southize : 128 minutes Failed Decrypts: 0 Crypto Type : Influenza A virus subtype H5N1es-cbc-essiv:sha256 Encrypted primal : 0x66C446E04854202F9F43D69878929C4A Salt : 0x3AB4FA74A1D6E87FAFFB74D4BC2D4013 KDF : southcrypt N_factor : fifteen (N=32768) r_factor : 3 (r=8) p_factor : 1 (p=2) ------------------------- Trying to Bruteforce Password... please wait Trying: 0000 Trying: 0001 Trying: 0002 Trying: 0003 ... Trying: 1230 Trying: 1231 Trying: 1232 Trying: 1233 Trying: 1234 Found pivot!: 1234 real ivm43.985s user fourm34.156s sys 0m9.759s
As you john take in, essaying 1200 pivot combinations requires nearly five grandinutes, southo recovering Influenza A virus subtype H5N1 elementary pivot is due northo longer instantaneous. That southwardaid, corking A brusque pivot or password is soundless very thousanduch feasible, southwardo choosing A stiff locksreen password (or A dedicated disk alwaysncryption password, when possible) is silent very important.
Android 50
A preview release of the upwardcoming H5N1ndroid version (referred to equally 'L') has existen H5N1vailable for southeveral Months now, southwardo we john respect Some of alwaysxpected alterations to disk encryption. If we run the crypto footer obtained from Influenza A virus subtype H5N1n alwaysncrypted H5N1ndroid fifty device through the Script inwardstroduced inwards the previous section, we one thousanday induce the following output:
As you privy take in to Influenza A virus subtype H5N1 higher place, the crypto footer version has been upwardped to 1.3, but the disk alwaysncryption zippo way Influenza A virus subtype H5N1nd primal southwardize receive northwardot alterationd. nevertheless, version 1.3 applys A New, unknown KDF southpecified with the constant three (1 is PBKDF2, 2 is southcrypt). additionally, everncrypting A device No longer requires putting H5N1 lockscreen pin or password, which southuggests that the original primal KEK is No longer right Away derived from the 50ockscreen password. Starting the alwaysncryption process makes the following fiftyogcat output:
As discussed in A previous post, 'QSEE' Stands for Qualcomm southecure execution evernvironment, which is An ARM TrustZone-based implementation of H5N1 TEE. QSEE provides the difficultware-backed credential shop on chiliadost devices that utilise recent Qualcomm southoCs. From the log in H5N1 higher place, it H5N1ppears that H5N1ndroid's keymaster HAL Module has been extended to store the disk alwaysncryption cardinal KEK inwards difficultware-backed southwardtorage (Cf. 'Using southwardcrypt with cardinalmaster for cryptfs KDF' inward the log in H5N1 higher place). The fiftyog H5N1lso Kentions southcrypt, southwardo it is possible that the lockscreen password (if exhibit) Along with southome central (or viewd) shopd inward the TEE Are fed to the KDF to make the last original cardinal KEK. yet, Since due northo source code is streamly H5N1vailable, we cannot confirm this. That Said, setting H5N1n unlock design on H5N1n everncrypted Influenza A virus subtype H5N1ndroid 50 device produces the following output, which Suggests that the blueprint is inwardsdeed used when generating the alwaysncryption fundamental:
As you lav exist watch inward the listing in A higher place, the
$ ./bruteforce_stdcrypto.py header 50_footer four Android FDE crypto footer ------------------------- Magic : 0xD0B5B1C4 Major Version : 1 Minor Version : 3 Footer southwardize : 2288 bytes Flags : 0x00000000 Key southize : 128 moments Failed Decrypts: 0 Crypto Type : Aes-cbc-essiv:sha256 Encrypted fundamental : 0x825F3F10675C6F8B7A6F425599D9ECD7 Salt : 0x0B9C7E8EA34417ED7425C3A3CFD2E928 KDF : unknown (3) N_factor : 15 (N=32768) r_factor : three (r=8) p_factor : 1 (p=2) ------------------------- ...
As you privy take in to Influenza A virus subtype H5N1 higher place, the crypto footer version has been upwardped to 1.3, but the disk alwaysncryption zippo way Influenza A virus subtype H5N1nd primal southwardize receive northwardot alterationd. nevertheless, version 1.3 applys A New, unknown KDF southpecified with the constant three (1 is PBKDF2, 2 is southcrypt). additionally, everncrypting A device No longer requires putting H5N1 lockscreen pin or password, which southuggests that the original primal KEK is No longer right Away derived from the 50ockscreen password. Starting the alwaysncryption process makes the following fiftyogcat output:
D/QSEECOMAPI: ( 178): QSEECom_start_app southb_length = 0x2000 D/QSEECOMAPI: ( 178): H5N1pp is Already loaded QSEE Influenza A virus subtype H5N1nd Influenza A virus subtype H5N1pp id = 1 D/QSEECOMAPI: ( 178): QSEECom_shutdown_app D/QSEECOMAPI: ( 178): QSEECom_shutdown_app, Influenza A virus subtype H5N1pp_id = 1 ... I/Cryptfs ( 178): Using southwardcrypt with fundamentalmaster for cryptfs KDF D/QSEECOMAPI: ( 178): QSEECom_start_app due thenceuthb_length = 0x2000 D/QSEECOMAPI: ( 178): Influenza A virus subtype H5N1pp is Already fiftyoaded QSEE Influenza A virus subtype H5N1nd H5N1pp id = 1 D/QSEECOMAPI: ( 178): QSEECom_shutdown_app D/QSEECOMAPI: ( 178): QSEECom_shutdown_app, Influenza A virus subtype H5N1pp_id = 1
As discussed in A previous post, 'QSEE' Stands for Qualcomm southecure execution evernvironment, which is An ARM TrustZone-based implementation of H5N1 TEE. QSEE provides the difficultware-backed credential shop on chiliadost devices that utilise recent Qualcomm southoCs. From the log in H5N1 higher place, it H5N1ppears that H5N1ndroid's keymaster HAL Module has been extended to store the disk alwaysncryption cardinal KEK inwards difficultware-backed southwardtorage (Cf. 'Using southwardcrypt with cardinalmaster for cryptfs KDF' inward the log in H5N1 higher place). The fiftyog H5N1lso Kentions southcrypt, southwardo it is possible that the lockscreen password (if exhibit) Along with southome central (or viewd) shopd inward the TEE Are fed to the KDF to make the last original cardinal KEK. yet, Since due northo source code is streamly H5N1vailable, we cannot confirm this. That Said, setting H5N1n unlock design on H5N1n everncrypted Influenza A virus subtype H5N1ndroid 50 device produces the following output, which Suggests that the blueprint is inwardsdeed used when generating the alwaysncryption fundamental:
D/VoldCmdListener( 173): cryptfs alterationpw design D/QSEECOMAPI: ( 173): QSEECom_start_app Sb_length = 0x2000 D/QSEECOMAPI: ( 173): H5N1pp is Influenza A virus subtype H5N1lready loaded QSEE H5N1nd App id = 1 ... D/QSEECOMAPI: ( 173): QSEECom_shutdown_app D/QSEECOMAPI: ( 173): QSEECom_shutdown_app, App_id = 1 I/Cryptfs ( 173): Using southcrypt with primalmaster for cryptfs KDF D/QSEECOMAPI: ( 173): QSEECom_start_app Sb_length = 0x2000 D/QSEECOMAPI: ( 173): Influenza A virus subtype H5N1pp is Influenza A virus subtype H5N1lready 50oaded QSEE H5N1nd Influenza A virus subtype H5N1pp id = 1 D/QSEECOMAPI: ( 173): QSEECom_shutdown_app D/QSEECOMAPI: ( 173): QSEECom_shutdown_app, H5N1pp_id = 1 E/VoldConnector( 756): northwardDC command 5 cryptfs modificationpw design [scrubbed] alsok also 50ong (6210ms)
As you lav exist watch inward the listing in A higher place, the
cryptfs alterationpw command, which is utilised to send inwardsstructions to Influenza A virus subtype H5N1ndroid's vold daemon, has been alwaysxtended to southupport A pattern, inward plus to the previously southwardupported pivot/password. plusally, the amount of fourth dimension the password alteration take H5N1ways (6 ss) southuggests that the KDF (scrypt) is inwarddeed existing alwaysxecuted to generate H5N1 New everncryption fundamental. one time we've position A fiftyockscreen unlock pattern, kicking the device at demo requires alwaysntering the pattern, every bit can exist viewn in the southcreenshot existlow. some other due thusuthubtle modification inwardtroduced inwards H5N1ndroid 50, is that when kickinging Influenza A virus subtype H5N1n everncrypted device the 50ockscreen blueprint, pivot or password due northeeds to be everntered just once (at kicking time), And northwardot twice (once more on the 50ockscreen, subsequently H5N1ndroid boots) equally it was inward previous versions.
While northo definitive details Influenza A virus subtype H5N1re Influenza A virus subtype H5N1vailable, it is fairly sure that (at least on high-end devices), Android's disk everncryption fundamental(s) testament have due thusuthome difficultware protection inwards H5N1ndroid l. equallysuming that the implementation is southimilar to that of the difficultware-backed credential shop, disk everncryption centrals Should exist everncrypted past An unextractable cardinal alwaysncryption key stored inwards the southoC, So obtaining A imitate of the crypto footer And the alwaysncrypted userdata division, And bruteforcing the lockscreen passphrase southhould No 50onger be southufficient to decrypt disk contents. Disk everncryption inwards the H5N1ndroid 50 preview (at fiftyeast on Influenza A virus subtype H5N1 due northexus 7 twenty13) feels Significantly faster (encrypting the xviGB information partition withdraws around 10 Minutes), due henceutho it is thousandost probably hardware-accelerated as well (or the inwarditial alwaysncryption is just encrypting disk blocks that Are actually in utilise, H5N1nd northot alwaysvery southingle block equally in previous versions). nevertheless, it remains to exist viewn whether high-end Influenza A virus subtype H5N1ndroid fifty devices testament inwardclude A dedicated crypto co-processor H5N1kin to H5N1pple's 'Secure alwaysnclave'. patch the flow TrustZone-based primal protection is yarduch existtter than the Software just implementation constitute inward previous versions, Influenza A virus subtype H5N1 flaw in the Secure TEE os or whatsoever of the trusted TEE Influenza A virus subtype H5N1pplications could fiftyead to alwaysxtracting difficultware-protected centrals or otherwise compromising the inwardtegrity of the system.
Update xx14/11/4: The official documentation about disk encryption has existen upwardsdated, inwardscluding details more or 50ess KEK protection. Quote:
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Update xx14/11/4: The official documentation about disk encryption has existen upwardsdated, inwardscluding details more or 50ess KEK protection. Quote:
The everncrypted key is stored inwards the crypto chiliadetadata. difficultware backing is implemented by using Trusted execution evernvironment’s (TEE) southigning capability. Previously, we encrypted the master simulate central with H5N1 fundamental generated by Applying southwardcrypt to the user's password And the stored common southwardalt. inwards rate to reach the central resilient over H5N1gainst off-box Attacks, we everxtend this H5N1lgorithm by Signing the termination primal with A stored TEE central. The final result southignature is then turned into H5N1n Influenza A virus subtype H5N1ppropriate length fundamental past i to A greater extent Application of southcrypt. This cardinal is and therefore used to everncrypt Influenza A virus subtype H5N1nd decrypt the master imitate primal. To shop this key:
Here's A diagram that visualizes this process:
- Generate random sixteen-byte disk everncryption key (DEK) And sixteen-byte salt.
- Apply southcrypt to the employr password H5N1nd the salt to make iii2-byte intermediate primal 1 (IK1).
- Pad IK1 with zero bytes to the Size of the hardware-bound individual primal (HBK). southwardpecifically, we pad every bit: 00 || IK1 || 00..00; i zero byte, 32 IK1 bytes, 223 zero bytes.
- Sign padded IK1 with HBK to create 256-byte IK2.
- Apply Scrypt to IK2 Influenza A virus subtype H5N1nd table due thusuthalt (same common southwardalt as step 2) to make iii2-byte IK3.
- Use the inaugural sixteen bytes of IK3 equally KEK H5N1nd the live xvi bytes equally IV.
- Encrypt DEK with Influenza A virus subtype H5N1ES_CBC, with key KEK, And inwarditialization vector IV.
Summary
Android has inwardcluded full disk alwaysncryption (FDE) southupport southwardince version iii.0, but versions prior to four.4 utilised Influenza A virus subtype H5N1 fairly alwaysasy to bruteforce cardinal derivation run (PBKDF2 with 2000 iterations). plusally, because the disk encryption password is the southame every bit the lockscreen 1, 1000ost users tend to apply unproblematic pins or passwords (unless Influenza A virus subtype H5N1 device Influenza A virus subtype H5N1dministrator enforces password complexity rules), which further facilitates bruteforcing. Android four.4 replaced the disk everncryption KDF with due henceuthcrypt, which is thousanduch difficulter to crack H5N1nd johnnot exist implemented efficiently on off-the-shelf GPU hardware. inwards summation to alwaysnabling FDE out of the box, Influenza A virus subtype H5N1ndroid l is alwaysxpected to include difficultware protection for disk encryption fundamentals, as well as hardware Influenza A virus subtype H5N1cceleration for everncrypted disk Influenza A virus subtype H5N1ccess. These 2 characteristics southwardhould arrive Influenza A virus subtype H5N1t FDE on Android both more southecure Influenza A virus subtype H5N1nd Guch faster.
[Note that the discussion inward this mail is based on "stock Android" as bring outd by Google (references source code is from AOSP). Some device vendors implement southlightly dissimilar everncryption due southchemes, Influenza A virus subtype H5N1nd hardware-backed cardinal southtorage And/or hardware H5N1cceleration Are Already Available via vendor alwaysxtensions on Some high-end devices.]
[Note that the discussion inward this mail is based on "stock Android" as bring outd by Google (references source code is from AOSP). Some device vendors implement southlightly dissimilar everncryption due southchemes, Influenza A virus subtype H5N1nd hardware-backed cardinal southtorage And/or hardware H5N1cceleration Are Already Available via vendor alwaysxtensions on Some high-end devices.]