crypto

MODULE

crypto

MODULE SUMMARY

Crypto Functions

DESCRIPTION

This module provides a set of cryptographic functions.

References:

• md5: The MD5 Message Digest Algorithm (RFC 1321)
  


• sha: Secure Hash Standard (FIPS 180-1)
  


• hmac: Keyed-Hashing for Message Authentication (RFC 2104)
  


• des: Data Encryption Standard (FIPS 46-2)
  


• ecb, cbc, cfb, ofb: DES modes of operation (FIPS 81).
  



Types

byte() = 0 ... 255
ioelem() = byte() | binary() | iolist()
iolist() = [ioelem()]
    

EXPORTS

start() -> ok

Starts the crypto server.

stop() -> ok

Stops the crypto server.

info() -> [atom()]

Stops the crypto server.

md5(Data) -> Digest

Types:
Data = iolist() | binary()
Digest = binary()

Computes an MD5 message digest from Data, where the length of the digest is 128 bits (16 bytes).

md5_init() -> Context

Types:
Context = binary()

Creates an MD5 context, to be used in subsequent calls to md5_update/2.

md5_update(Context, Data) -> NewContext

Types:
Data = iolist() | binary()
Context = NewContext = binary()

Updates an MD5 Context with Data, and returns a NewContext.

md5_final(Context) -> Digest

Types:
Context = Digest = binary()

Finishes the update of an MD5 Context and returns the computed MD5 message digest.

sha(Data) -> Digest

Types:
Data = iolist() | binary()
Digest = binary()

Computes an SHA message digest from Data, where the length of the digest is 160 bits (20 bytes).

sha_init() -> Context

Types:
Context = binary()

Creates an SHA context, to be used in subsequent calls to sha_update/2.

sha_update(Context, Data) -> NewContext

Types:
Data = iolist() | binary()
Context = NewContext = binary()

Updates an SHA Context with Data, and returns a NewContext.

sha_final(Context) -> Digest

Types:
Context = Digest = binary()

Finishes the update of an SHA Context and returns the computed SHA message digest.

md5_mac(Key, Data) -> Mac

Types:
Key = Data = iolist() | binary()
Mac = binary()

Computes an MD5 MAC message authentification code from Key and Data, where the the length of the Mac is 128 bits (16 bytes).

md5_mac_96(Key, Data) -> Mac

Types:
Key = Data = iolist() | binary()
Mac = binary()

Computes an MD5 MAC message authentification code from Key and Data, where the length of the Mac is 96 bits (12 bytes).

sha_mac(Key, Data) -> Mac

Types:
Key = Data = iolist() | binary()
Mac = binary()

Computes an SHA MAC message authentification code from Key and Data, where the length of the Mac is 160 bits (20 bytes).

sha_mac_96(Key, Data) -> Mac

Types:
Key = Data = iolist() | binary()
Mac = binary()

Computes an SHA MAC message authentification code from Key and Data, where the length of the Mac is 96 bits (12 bytes).

des_cbc_encrypt(Key, IVec, Text) -> Cipher

Types:
Key = Text = iolist() | binary()
IVec = Cipher = binary()

Encrypts Text according to DES in CBC mode. Text must be a multiple of 64 bits (8 bytes). Key is the DES key, and IVec is an arbitrary initializing vector. The lengths of Key and IVec must be 64 bits (8 bytes).

des_cbc_decrypt(Key, IVec, Cipher) -> Text

Types:
Key = Cipher = iolist() | binary()
IVec = Text = binary()

Decrypts Cipher according to DES in CBC mode. Key is the DES key, and IVec is an arbitrary initializing vector. Key and IVec must have the same values as those used when encrypting. Cipher must be a multiple of 64 bits (8 bytes). The lengths of Key and IVec must be 64 bits (8 bytes).

DES in CBC mode

The Data Encryption Standard (DES) defines an algoritm for encrypting and decrypting an 8 byte quantity using an 8 byte key (actually only 56 bits of the key is used).

When it comes to encrypting and decrypting blocks that are multiples of 8 bytes various modes are defined (FIPS 81). One of those modes is the Cipher Block Chaining (CBC) mode, where the encryption of an 8 byte segment depend not only of the contents of the segment itself, but also on the result of encrypting the previous segment: the encryption of the previous segment becomes the initializing vector of the encryption of the current segment.

Thus the encryption of every segment depends on the encryption key (which is secret) and the encryption of the previous segment, except the first segment which has to be provided with a first initializing vector. That vector could be chosen at random, or be counter of some kind. It does not have to be secret.

The following example is drawn from the FIPS 81 standard, where both the plain text and the resulting cipher text is settled. We use the Erlang bitsyntax to define binary literals. The following Erlang code fragment returns `true'.

      Key = <<16#01,16#23,16#45,16#67,16#89,16#ab,16#cd,16#ef>>,
      IVec = <<16#12,16#34,16#56,16#78,16#90,16#ab,16#cd,16#ef>>,
      P = "Now is the time for all ",
      C = crypto:des_cbc_encrypt(K, I, P),
      C == <<16#e5,16#c7,16#cd,16#de,16#87,16#2b,16#f2,16#7c,
             16#43,16#e9,16#34,16#00,16#8c,16#38,16#9c,16#0f,
             16#68,16#37,16#88,16#49,16#9a,16#7c,16#05,16#f6>>,
      <<"Now is the time for all ">> == crypto:des_cbc_decrypt(Key,IVec,C).

    

The following is true for the DES CBC mode. For all decompositions P1 ++ P2 = P of a plain text message P (where the length of all quantities are multiples of 8 bytes), the encryption C of P is equal to C1 ++ C2, where C1 is obtained by encrypting P1 with Key and the initializing vector IVec, and where C2 is obtained by encrypting P2 with Key and the initializing vector l(C1), where l(B) denotes the last 8 bytes of the binary B.

Similarly, for all decompositions C1 ++ C2 = C of a cipher text message C (where the length of all quantities are multiples of 8 bytes), the decryption P of C is equal to P1 ++ P2, where P1 is obtained by decrypting C1 with Key and the initializing vector IVec, and where P2 is obtained by decrypting C2 with Key and the initializing vector l(C1), where l(.) is as above.

AUTHORS

Peter Högfeldt - support@erlang.ericsson.se