Dh C Reference Documentation

Dh

Current Version: 9.5.0.73

Diffie-Hellman key-exchange component.

Diffie-Hellman (D-H) key exchange is a cryptographic protocol that allows two parties that have no prior knowledge of each other to jointly establish a shared secret key over an insecure communications channel. This key can then be used to encrypt subsequent communications using a symmetric key cipher.

Synonyms of Diffie-Hellman key exchange include:

  • Diffie-Hellman key agreement
  • Diffie-Hellman key establishment
  • Diffie-Hellman key negotiation
  • exponential key exchange

Create/Dispose

HCkDh instance = CkDh_Create();
// ...
CkDh_Dispose(instance);
HCkDh CkDh_Create(void);

Creates an instance of the HCkDh object and returns a handle ("void *" pointer). The handle is passed in the 1st argument for the functions listed on this page.

void CkDh_Dispose(HCkDh handle);

Objects created by calling CkDh_Create must be freed by calling this method. A memory leak occurs if a handle is not disposed by calling this function. Also, any handle returned by a Chilkat "C" function must also be freed by the application by calling the appropriate Dispose method, such as CkDh_Dispose.

Properties

DebugLogFilePath
void CkDh_getDebugLogFilePath(HCkDh cHandle, HCkString retval);
void CkDh_putDebugLogFilePath(HCkDh cHandle, const char *newVal);
const char *CkDh_debugLogFilePath(HCkDh cHandle);

If set to a file path, causes each Chilkat method or property call to automatically append it's LastErrorText to the specified log file. The information is appended such that if a hang or crash occurs, it is possible to see the context in which the problem occurred, as well as a history of all Chilkat calls up to the point of the problem. The VerboseLogging property can be set to provide more detailed information.

This property is typically used for debugging the rare cases where a Chilkat method call hangs or generates an exception that halts program execution (i.e. crashes). A hang or crash should generally never happen. The typical causes of a hang are:

  1. a timeout related property was set to 0 to explicitly indicate that an infinite timeout is desired,
  2. the hang is actually a hang within an event callback (i.e. it is a hang within the application code), or
  3. there is an internal problem (bug) in the Chilkat code that causes the hang.

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G
int CkDh_getG(HCkDh cHandle);

The generator. The value of G should be either 2 or 5.

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LastErrorHtml
void CkDh_getLastErrorHtml(HCkDh cHandle, HCkString retval);
const char *CkDh_lastErrorHtml(HCkDh cHandle);

Provides information in HTML format about the last method/property called. If a method call returns a value indicating failure, or behaves unexpectedly, examine this property to get more information.

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LastErrorText
void CkDh_getLastErrorText(HCkDh cHandle, HCkString retval);
const char *CkDh_lastErrorText(HCkDh cHandle);

Provides information in plain-text format about the last method/property called. If a method call returns a value indicating failure, or behaves unexpectedly, examine this property to get more information.

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LastErrorXml
void CkDh_getLastErrorXml(HCkDh cHandle, HCkString retval);
const char *CkDh_lastErrorXml(HCkDh cHandle);

Provides information in XML format about the last method/property called. If a method call returns a value indicating failure, or behaves unexpectedly, examine this property to get more information.

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LastMethodSuccess
BOOL CkDh_getLastMethodSuccess(HCkDh cHandle);
void CkDh_putLastMethodSuccess(HCkDh cHandle, BOOL newVal);
Introduced in version 9.5.0.52

Indicate whether the last method call succeeded or failed. A value of TRUE indicates success, a value of FALSE indicates failure. This property is automatically set for method calls. It is not modified by property accesses. The property is automatically set to indicate success for the following types of method calls:

  • Any method that returns a string.
  • Any method returning a Chilkat object, binary bytes, or a date/time.
  • Any method returning a standard boolean status value where success = TRUE and failure = FALSE.
  • Any method returning an integer where failure is defined by a return value less than zero.

Note: Methods that do not fit the above requirements will always set this property equal to TRUE. For example, a method that returns no value (such as a "void" in C++) will technically always succeed.

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P
void CkDh_getP(HCkDh cHandle, HCkString retval);
const char *CkDh_p(HCkDh cHandle);

A "safe" large prime returned as a hex string. The hex string represent a bignum in SSH1 format.

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Utf8
BOOL CkDh_getUtf8(HCkDh cHandle);
void CkDh_putUtf8(HCkDh cHandle, BOOL newVal);

When set to TRUE, all "const char *" arguments are interpreted as utf-8 strings. If set to FALSE (the default), then "const char *" arguments are interpreted as ANSI strings. Also, when set to TRUE, and Chilkat method returning a "const char *" is returning the utf-8 representation. If set to FALSE, all "const char *" return values are ANSI strings.

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VerboseLogging
BOOL CkDh_getVerboseLogging(HCkDh cHandle);
void CkDh_putVerboseLogging(HCkDh cHandle, BOOL newVal);

If set to TRUE, then the contents of LastErrorText (or LastErrorXml, or LastErrorHtml) may contain more verbose information. The default value is FALSE. Verbose logging should only be used for debugging. The potentially large quantity of logged information may adversely affect peformance.

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Version
void CkDh_getVersion(HCkDh cHandle, HCkString retval);
const char *CkDh_version(HCkDh cHandle);

Version of the component/library, such as "9.5.0.63"

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Methods

CreateE
BOOL CkDh_CreateE(HCkDh cHandle, int numBits, HCkString outStr);
const char *CkDh_createE(HCkDh cHandle, int numBits);

The 1st step in Diffie-Hellman key exchange (to generate a shared-secret). The numBits should be twice the size (in bits) of the shared secret to be generated. For example, if you are using DH to create a 128-bit AES session key, then numBits should be set to 256. Returns E as a bignum in SSH-format as a hex string.

Returns TRUE for success, FALSE for failure.

More Information and Examples
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FindK
BOOL CkDh_FindK(HCkDh cHandle, const char *E, HCkString outStr);
const char *CkDh_findK(HCkDh cHandle, const char *E);

The 2nd and final step in Diffie-Hellman (DH) key exchange. E is the E created by the other party. Returns the shared secret (K) as an SSH1-format bignum encoded as a hex string.

Returns TRUE for success, FALSE for failure.

More Information and Examples
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GenPG
BOOL CkDh_GenPG(HCkDh cHandle, int numBits, int G);

Generates a large safe prime that is numBits bits in size using the generator G. Generating a new (random) P is expensive in both time and CPU cycles. A prime should be 1024 or more bits in length.

Returns TRUE for success, FALSE for failure.

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SaveLastError
BOOL CkDh_SaveLastError(HCkDh cHandle, const char *path);

Saves the last-error information (the contents of LastErrorXml) to an XML formatted file.

Returns TRUE for success, FALSE for failure.

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SetPG
BOOL CkDh_SetPG(HCkDh cHandle, const char *p, int g);

Sets explicit values for P and G. Returns TRUE if P and G conform to the requirements for Diffie-Hellman. P is an SSH1-format bignum passed as a hexidecimalized string.

Returns TRUE for success, FALSE for failure.

More Information and Examples
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UnlockComponent
BOOL CkDh_UnlockComponent(HCkDh cHandle, const char *unlockCode);

Unlocks the component. This must be called once prior to calling any other method. A fully-functional 30-day trial is automatically started when an arbitrary string is passed to this method. For example, passing "Hello", or "abc123" will unlock the component for the 1st thirty days after the initial install.

Returns TRUE for success, FALSE for failure.

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UseKnownPrime
void CkDh_UseKnownPrime(HCkDh cHandle, int index);

Sets P and G to a known safe prime. The index may have the following values:

1: First Oakley Default Group from RFC2409, section 6.1. Generator is 2. The prime is: 2^768 - 2 ^704 - 1 + 2^64 * { [2^638 pi] + 149686 }

2: Prime for 2nd Oakley Group (RFC 2409) -- 1024-bit MODP Group. Generator is 2. The prime is: 2^1024 - 2^960 - 1 + 2^64 * { [2^894 pi] + 129093 }.

3: 1536-bit MODP Group from RFC3526, Section 2. Generator is 2. The prime is: 2^1536 - 2^1472 - 1 + 2^64 * { [2^1406 pi] + 741804 }

4: Prime for 14th Oakley Group (RFC 3526) -- 2048-bit MODP Group. Generator is 2. The prime is: 2^2048 - 2^1984 - 1 + 2^64 * { [2^1918 pi] + 124476 }

5: 3072-bit MODP Group from RFC3526, Section 4. Generator is 2. The prime is: 2^3072 - 2^3008 - 1 + 2^64 * { [2^2942 pi] + 1690314 }

6: 4096-bit MODP Group from RFC3526, Section 5. Generator is 2. The prime is: 2^4096 - 2^4032 - 1 + 2^64 * { [2^3966 pi] + 240904 }

7: 6144-bit MODP Group from RFC3526, Section 6. Generator is 2. The prime is: 2^6144 - 2^6080 - 1 + 2^64 * { [2^6014 pi] + 929484 }

8: 8192-bit MODP Group from RFC3526, Section 7. Generator is 2. The prime is: 2^8192 - 2^8128 - 1 + 2^64 * { [2^8062 pi] + 4743158 }

More Information and Examples
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