An AES-128 expects a key of 128 bit, 16 byte. To generate such a key, use OpenSSL as: openssl rand 16 myaes.key AES-256 expects a key of 256 bit, 32 byte. To generate such a key, use OpenSSL as: openssl rand 16 myaes.key AES-256 expects a key of 256 bit, 32 byte.
- There are multiple ways of generating an encryption key. Most implementations rely on a random object. All examples mentioned here use a secure cryptographic randomizer.
- Use PBKDF2 to generate a 256-bit key from your password and the salt, then split that into two 128-bit keys (k2, k3). Make sure your algorithm's native output is at least 256 bits, or this will be slow. PBKDF2- SHA256 is a good choice.
| Perfect Passwords GRC's Ultra High Security Password Generator |
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| 2,618 sets of passwords generated per day 33,542,661 sets of passwords generated for our visitors |
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not simple. So here is some totally random raw material, generated just for YOU, to start with. |
64 random hexadecimal characters (0-9 and A-F):
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63 random printable ASCII characters:
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63 random alpha-numeric characters (a-z, A-Z, 0-9):
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| Click your web browser's 'refresh' button a few times and watch the password strings change each time.What makes these perfect and safe?
Also, because this page will only allow itself to be displayed over a snoop-proof and proxy-proof high-security SSL connection, and it is marked as having expired back in 1999, this page which was custom generated just now for you will not be cached or visible to anyone else. Therefore, these password strings are just for you. No one else can ever see them or get them. You may safely take these strings as they are, or use chunks from several to build your own if you prefer, or do whatever you want with them. Each set displayed are totally, uniquely yours — forever. The 'Application Notes' section below discusses various aspects of using these random passwords for locking down wireless WEP and WPA networks, for use as VPN shared secrets, as well as for other purposes. The 'Techie Details' section at the end describes exactly how these super-strong maximum-entropy passwords are generated (to satisfy the uber-geek inside you). |
Application Notes: A note about 'random' and 'pseudo-random' terminology: There are ways to generate absolutely random numbers, but computer algorithms cannot be used for that, since, by definition, no deterministic mathematical algorithm can generate a random result. Electrical and mechanical noise found in chaotic physical systems can be tapped and used as a source of true randomness, but this is much more than is needed for our purposes here. High quality algorithms are sufficient. The deterministic binary noise generated by my server, which is then converted into various displayable formats, is derived from the highest quality mathematical pseudo-random algorithms known. In other words, these password strings are as random as anything non-random can be. This page's password 'raw material': |
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| Each of the 64 hexadecimal characters encodes 4 bits of binary data, so the entire 64 characters is equivalent to 256 binary bits — which is the actual binary key length used by the WiFi WPA pre-shared key (PSK). Some WPA-PSK user interfaces (such as the one in Windows XP) allows the 256-bit WPA pre-shared key to be directly provided as 64 hexadecimal characters. This is a precise means for supplying the WPA keying material, but it is ONLY useful if ALL of the devices in a WPA-protected WiFi network allow the 256-bit keying material to be specified as raw hex. If any device did not support this mode of specification (and most do not) it would not be able to join the network.
Using fewer hex characters for WEP encryption: WEP key strength (key length) is sometimes confusing because, although there are only two widely accepted standard lengths, 40-bit and 104-bit, those lengths are sometimes confused by adding the 24-bit IV (initialization vector) counter to the length, resulting in 64-bit and 128-bit total key lengths. However, the user only ever specifies a key of either 40 or 104 binary bits. Since WEP keys should always be specified in their hexadecimal form to guarantee device interaction, and since each hex digit represents 4 binary bits of the key, 40 and 104 bit keys are represented by 10 and 26 hex digits respectively. So you may simply snip off whatever length of random hex characters you require for your system's WEP key. Note that if all of your equipment supports the use of the new longer 256/232 bit WEP keys, you would use 232/4 or 58 hexadecimal characters for your pre-shared key. 63 printable ASCII characters hashed down to 256 binary bits: |
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| The more 'standard' means for specifying the 256-bits of WPA keying material is for the user to specify a string of up to 63 printable ASCII characters. This string is then 'hashed' along with the network's SSID designation to form a cryptographically strong 256-bit result which is then used by all devices within the WPA-secured WiFi network. (The ASCII character set was updated to remove SPACE characters since a number of WPA devices were not handling spaces as they should.) The 63 alphanumeric-only character subset: |
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| If some device was not following the WiFi Alliance WPA specification by not hashing the entire printable ASCII character set correctly, it would end up with a different 256-bit hash result than devices that correctly obeyed the specification. It would then be unable to connect to any network that uses the full range of printable ASCII characters.
Since we have heard unconfirmed anecdotal reports of such non-compliant WPA devices (and since you might have one), this page also offers 'junior' WPA password strings using only the 'easy' ASCII characters which even any non-fully-specification-compliant device would have to be able to properly handle. If you find that using the full random ASCII character set within your WPA-PSK protected WiFi network causes one of your devices to be unable to connect to your WPA protected access point, you can downgrade your WPA network to 'easy ASCII' by using one of these easy keys. And don't worry for a moment about using an easy ASCII key. If you still use a full-length 63 character key, your entire network will still be EXTREMELY secure. And PLEASE drop us a line to let us know that you have such a device and what it is!
When these passwords are used to generate pre-shared keys for protecting WPA WiFi and VPN networks, the only known attack is the use of 'brute force' — trying every possible password combination. Brute force attackers hope that the network's designer (you) were lazy and used a shorter password for 'convenience'. So they start by trying all one-character passwords, then two-character, then three and so on, working their way up toward longer random passwords.
Note that while this 'the longer the better' rule of thumb is always true, long passwords won't protect legacy WEP-protected networks due to well known and readily exploited weaknesses in the WEP keying system and its misuse of WEP's RC4 encryption. With WEP protection, even a highly random maximum-entropy key can be cracked in a few hours. (Listen to Security Now! episode #11 for the full story on cracking WEP security.) The Techie Details: Since its introduction, this Perfect Passwords page has generated a great deal of interest. A number of people have wished to duplicate this page on their own sites, and others have wanted to know exactly how these super-strong and guaranteed-to-be-unique never repeating passwords are generated. The following diagram and discussion provides full disclosure of the pseudo-random number generating algorithm I employed to create the passwords on this page: |
While the diagram above might at first seem a bit confusing, it is a common and well understood configuration of standard cryptographic elements. A succinct written description of the algorithm would read: 'Rijndael (AES) block encryption of never-repeating counter values in CBC mode.' CBC stands for 'Cipher Block Chaining' and, as I describe in detail in the second half of Security Now! Episode #107, CBC provides necessary security in situations where some repetition or predictability of the 'plaintext' message is present. Since the 'plaintext' in this instance is a large 128-bit steadily-increasing (monotonic) counter value (which gives us our guaranteed never-to-repeat property, but is also extremely predictable) we need to scramble it so that the value being encrypted cannot be predicted. This is what 'CBC' does: As the diagram above shows, the output from the previous encryption operation is 'fed back' and XOR-mixed with the incrementing counter value. This prevents the possibility of determining the secret key by analysing successive counter encryption results. One last detail: Since there is no 'output from the previous encryption' to be used during the encryption of the first block, the switch shown in the diagram above is used to supply a 128-bit 'Initialization Vector' (which is just 128-bits of secret random data) for the XOR-mixing of the first counter value. Thus, the first encryption is performed on a mixture of the 128-bit counter and the 'Initialization Vector' value, and subsequent encryptions are performed on the mixture of the incrementing counter and the previous encrypted result. The result of the combination of the 256-bit Rijndael/AES secret key, the unknowable (therefore secret) present value of the 128-bit monotonically incrementing counter, and the 128-bit secret Initialization Vector (IV) is 512-bits of secret data providing extremely high security for the generation of this page's 'perfect passwords'. No one is going to figure out what passwords you have just received. How much security do 512 binary bits provide? Well, 2^512 (2 raised to the power of 512) is the total number of possible combinations of those 512 binary bits — every single bit of which actively participates in determining this page's successive password sequence. 2^512 is approximately equal to: 1.34078079 x 10^154, which is this rather amazing number:
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Gibson Research Corporation is owned and operated by Steve Gibson. The contents
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AES uses a key schedule to expand a short key into a number of separate round keys. The three AES variants have a different number of rounds. Each variant requires a separate 128-bit round key for each round plus one more.[note 1] The key schedule produces the needed round keys from the initial key.
Round constants[edit]
| i | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
|---|---|---|---|---|---|---|---|---|---|---|
| rci | 01 | 02 | 04 | 08 | 10 | 20 | 40 | 80 | 1B | 36 |
The round constant rconi for round i of the key expansion is the 32-bit word:
- rconi=[rci001600160016]{displaystyle rcon_{i}={begin{bmatrix}rc_{i}&00_{16}&00_{16}&00_{16}end{bmatrix}}}
where rci is an eight-bit value defined as:
Openssl Generate 256 Bit Key
- rci={1if i=12⋅rci−1if i>1 and rci−1<8016(2⋅rci−1)⊕1B16if i>1 and rci−1≥8016{displaystyle rc_{i}={begin{cases}1&{text{if }}i=12cdot rc_{i-1}&{text{if }}i>1{text{ and }}rc_{i-1}<80_{16}(2cdot rc_{i-1})oplus {text{1B}}_{16}&{text{if }}i>1{text{ and }}rc_{i-1}geq 80_{16}end{cases}}}
where ⊕{displaystyle oplus } is the bitwise XOR operator and constants such as 0016 and 1B16 are given in hexadecimal. Equivalently:
- rci=xi−1{displaystyle rc_{i}=x^{i-1}}
where the bits of rci are treated as the coefficients of an element of the finite fieldGF(2)[x]/(x8+x4+x3+x+1){displaystyle {rm {{GF}(2)[x]/(x^{8}+x^{4}+x^{3}+x+1)}}}, so that e.g. rc10=3616=001101102{displaystyle rc_{10}=36_{16}=00110110_{2}} represents the polynomial x5+x4+x2+x{displaystyle x^{5}+x^{4}+x^{2}+x}.
AES uses up to rcon10 for AES-128 (as 11 round keys are needed), up to rcon8 for AES-192, and up to rcon7 for AES-256.[note 2]
The key schedule[edit]
Define:
- N as the length of the key in 32-bit words: 4 words for AES-128, 6 words for AES-192, and 8 words for AES-256
- K0, K1, ... KN-1 as the 32-bit words of the original key
- R as the number of round keys needed: 11 round keys for AES-128, 13 keys for AES-192, and 15 keys for AES-256[note 3]
- W0, W1, ... W4R-1 as the 32-bit words of the expanded key[note 4]
Also define RotWord as a one-byte left circular shift:
- RotWord([b0b1b2b3])=[b1b2b3b0]{displaystyle operatorname {RotWord} ({begin{bmatrix}b_{0}&b_{1}&b_{2}&b_{3}end{bmatrix}})={begin{bmatrix}b_{1}&b_{2}&b_{3}&b_{0}end{bmatrix}}}
and SubWord as an application of the AES S-box to each of the four bytes of the word:
- SubWord([b0b1b2b3])=[S(b0)S(b1)S(b2)S(b3)]{displaystyle operatorname {SubWord} ({begin{bmatrix}b_{0}&b_{1}&b_{2}&b_{3}end{bmatrix}})={begin{bmatrix}operatorname {S} (b_{0})&operatorname {S} (b_{1})&operatorname {S} (b_{2})&operatorname {S} (b_{3})end{bmatrix}}}
Aes Key Generator
Then for i=0…4R−1{displaystyle i=0ldots 4R-1}:
- Wi={Kiif i<NWi−N⊕SubWord(RotWord(Wi−1))⊕rconi/Nif i≥N and i≡0(modN)Wi−N⊕SubWord(Wi−1)if i≥N, N>6, and i≡4(modN)Wi−N⊕Wi−1otherwise.{displaystyle W_{i}={begin{cases}K_{i}&{text{if }}i<NW_{i-N}oplus operatorname {SubWord} (operatorname {RotWord} (W_{i-1}))oplus rcon_{i/N}&{text{if }}igeq N{text{ and }}iequiv 0{pmod {N}}W_{i-N}oplus operatorname {SubWord} (W_{i-1})&{text{if }}igeq N{text{, }}N>6{text{, and }}iequiv 4{pmod {N}}W_{i-N}oplus W_{i-1}&{text{otherwise.}}end{cases}}}
Notes[edit]
- ^Non-AES Rijndael variants require up to 256 bits of expanded key per round
- ^The Rijndael variants with larger block sizes use more of these constants, up to rcon29 for Rijndael with 128-bit keys and 256 bit blocks (needs 15 round keys of each 256 bit, which means 30 full rounds of key expansion, which means 29 calls to the key schedule core using the round constants). The remaining constants for i ≥ 11 are: 6C, D8, AB, 4D, 9A, 2F, 5E, BC, 63, C6, 97, 35, 6A, D4, B3, 7D, FA, EF and C5
- ^Other Rijndael variants require max(N, B) + 7 round keys, where B is the block size in words
- ^Other Rijndael variants require BR words of expanded key, where B is the block size in words
References[edit]
- FIPS PUB 197: the official AES standard (PDF file)
Aes 256 Encryption Key
External links[edit]
Tps Aes Key
- schematic view of the key schedule for 128 and 256 bit keysfor 160-bit keys on Cryptography Stack Exchange
Generate 256 Bit Aes Key C#