BCryptDeriveKey function (bcrypt.h)
The BCryptDeriveKey function derives a key from a secret agreement value.
For key derivation from a given secret, see BCryptKeyDerivation.
Syntax
NTSTATUS BCryptDeriveKey(
[in] BCRYPT_SECRET_HANDLE hSharedSecret,
[in] LPCWSTR pwszKDF,
[in, optional] BCryptBufferDesc *pParameterList,
[out, optional] PUCHAR pbDerivedKey,
[in] ULONG cbDerivedKey,
[out] ULONG *pcbResult,
[in] ULONG dwFlags
);
Parameters
[in] hSharedSecret
The secret agreement handle to create the key from. This handle is obtained from the BCryptSecretAgreement function.
[in] pwszKDF
A pointer to a null-terminated Unicode string that identifies the key derivation function (KDF) to use to derive the key. This can be one of the following strings.
BCRYPT_KDF_HASH (L"HASH")
Use the hash key derivation function.
If the cbDerivedKey parameter is less than the size of the derived key, this function will only copy the specified number of bytes to the pbDerivedKey buffer. If the cbDerivedKey parameter is greater than the size of the derived key, this function will copy the key to the pbDerivedKey buffer and set the variable pointed to by the pcbResult to the actual number of bytes copied.
The parameters identified by the pParameterList parameter either can or must contain the following parameters, as indicated by the Required or optional column.
| Parameter | Description | Required or optional |
|---|---|---|
| KDF_HASH_ALGORITHM |
A null-terminated Unicode string that identifies the hash algorithm to use. This can be one of the standard hash algorithm identifiers from CNG Algorithm Identifiers or the identifier for another registered hash algorithm.
If this parameter is not specified, the SHA1 hash algorithm is used. |
Optional |
| KDF_SECRET_PREPEND | A value to add to the beginning of the message input to the hash function. For more information, see Remarks. | Optional |
| KDF_SECRET_APPEND | A value to add to the end of the message input to the hash function. For more information, see Remarks. | Optional |
The call to the KDF is made as shown in the following pseudocode.
KDF-Prepend = KDF_SECRET_PREPEND[0] +
KDF_SECRET_PREPEND[1] +
... +
KDF_SECRET_PREPEND[n]
KDF-Append = KDF_SECRET_APPEND[0] +
KDF_SECRET_APPEND[1] +
... +
KDF_SECRET_APPEND[n]
KDF-Output = Hash(
KDF-Prepend +
hSharedSecret +
KDF-Append)
BCRYPT_KDF_HMAC (L"HMAC")
Use the Hash-Based Message Authentication Code (HMAC) key derivation function.
If the cbDerivedKey parameter is less than the size of the derived key, this function will only copy the specified number of bytes to the pbDerivedKey buffer. If the cbDerivedKey parameter is greater than the size of the derived key, this function will copy the key to the pbDerivedKey buffer and set the variable pointed to by the pcbResult to the actual number of bytes copied.
The parameters identified by the pParameterList parameter either can or must contain the following parameters, as indicated by the Required or optional column.
| Parameter | Description | Required or optional |
|---|---|---|
| KDF_HASH_ALGORITHM |
A null-terminated Unicode string that identifies the hash algorithm to use. This can be one of the standard hash algorithm identifiers from CNG Algorithm Identifiers or the identifier for another registered hash algorithm.
If this parameter is not specified, the SHA1 hash algorithm is used. |
Optional |
| KDF_HMAC_KEY | The key to use for the pseudo-random function (PRF). | Optional |
| KDF_SECRET_PREPEND | A value to add to the beginning of the message input to the hash function. For more information, see Remarks. | Optional |
| KDF_SECRET_APPEND | A value to add to the end of the message input to the hash function. For more information, see Remarks. | Optional |
The call to the KDF is made as shown in the following pseudocode.
KDF-Prepend = KDF_SECRET_PREPEND[0] +
KDF_SECRET_PREPEND[1] +
... +
KDF_SECRET_PREPEND[n]
KDF-Append = KDF_SECRET_APPEND[0] +
KDF_SECRET_APPEND[1] +
... +
KDF_SECRET_APPEND[n]
KDF-Output = HMAC-Hash(
KDF_HMAC_KEY,
KDF-Prepend +
hSharedSecret +
KDF-Append)
BCRYPT_KDF_TLS_PRF (L"TLS_PRF")
Use the transport layer security (TLS) pseudo-random function (PRF) key derivation function. The size of the derived key is always 48 bytes, so the cbDerivedKey parameter must be 48.
The parameters identified by the pParameterList parameter either can or must contain the following parameters, as indicated by the Required or optional column.
| Parameter | Description | Required or optional |
|---|---|---|
| KDF_TLS_PRF_LABEL | An ANSI string that contains the PRF label. | Required |
| KDF_TLS_PRF_SEED | The PRF seed. The seed must be 64 bytes long. | Required |
| KDF_TLS_PRF_PROTOCOL |
A DWORD value that specifies the TLS protocol version whose PRF algorithm is to be used.
Valid values are:
Windows Server 2008 and Windows Vista: TLS1_1_PROTOCOL_VERSION, TLS1_2_PROTOCOL_VERSION and DTLS1_0_PROTOCOL_VERSION are not supported. Windows Server 2008 R2, Windows 7, Windows Server 2008 and Windows Vista: DTLS1_0_PROTOCOL_VERSION is not supported. |
Optional |
| KDF_HASH_ALGORITHM | The CNG algorithm ID of the hash to be used with the HMAC in the PRF, for the TLS 1.2 protocol version. Valid choices are SHA-256 and SHA-384. If not specified, SHA-256 is used. | Optional |
The call to the KDF is made as shown in the following pseudocode.
KDF-Output = PRF(
hSharedSecret,
KDF_TLS_PRF_LABEL,
KDF_TLS_PRF_SEED)
BCRYPT_KDF_SP80056A_CONCAT (L"SP800_56A_CONCAT")
Use the SP800-56A key derivation function.
The parameters identified by the pParameterList parameter either can or must contain the following parameters, as indicated by the Required or optional column. All parameter values are treated as opaque byte arrays.
| Parameter | Description | Required or optional |
|---|---|---|
| KDF_ALGORITHMID | Specifies the AlgorithmID subfield of the OtherInfo field in the SP800-56A key derivation function. Indicates the intended purpose of the derived key. | Required |
| KDF_PARTYUINFO | Specifies the PartyUInfo subfield of the OtherInfo field in the SP800-56A key derivation function. The field contains public information contributed by the initiator. | Required |
| KDF_PARTYVINFO | Specifies the PartyVInfo subfield of the OtherInfo field in the SP800-56A key derivation function. The field contains public information contributed by the responder. | Required |
| KDF_SUPPPUBINFO | Specifies the SuppPubInfo subfield of the OtherInfo field in the SP800-56A key derivation function. The field contains public information known to both initiator and responder. | Optional |
| KDF_SUPPPRIVINFO | Specifies the SuppPrivInfo subfield of the OtherInfo field in the SP800-56A key derivation function. It contains private information known to both initiator and responder, such as a shared secret. | Optional |
The call to the KDF is made as shown in the following pseudocode.
KDF-Output = SP_800-56A_KDF(
hSharedSecret,
KDF_ALGORITHMID,
KDF_PARTYUINFO,
KDF_PARTYVINFO,
KDF_SUPPPUBINFO,
KDF_SUPPPRIVINFO)
Windows Server 2008, Windows Vista, Windows Server 2003 and Windows XP: This value is not supported.
BCRYPT_KDF_RAW_SECRET (L"TRUNCATE")
Returns the little-endian representation of the raw secret without any modification.
If the cbDerivedKey parameter is less than the size of the derived key, this function will only copy the specified number of bytes to the pbDerivedKey buffer. If the cbDerivedKey parameter is greater than the size of the derived key, this function will copy the key to the pbDerivedKey buffer and set the variable pointed to by the pcbResult to the actual number of bytes copied.
Windows 8, Windows Server 2008, Windows Vista, Windows Server 2003 and Windows XP: This value is not supported.
[in, optional] pParameterList
The address of a BCryptBufferDesc structure that contains the KDF parameters. This parameter is optional and can be NULL if it is not needed.
[out, optional] pbDerivedKey
The address of a buffer that receives the key. The cbDerivedKey parameter contains the size of this buffer. If this parameter is NULL, this function will place the required size, in bytes, in the ULONG pointed to by the pcbResult parameter.
[in] cbDerivedKey
The size, in bytes, of the pbDerivedKey buffer.
[out] pcbResult
A pointer to a ULONG that receives the number of bytes that were copied to the pbDerivedKey buffer. If the pbDerivedKey parameter is NULL, this function will place the required size, in bytes, in the ULONG pointed to by this parameter.
[in] dwFlags
A set of flags that modify the behavior of this function. This can be zero or the following value.
Return value
Returns a status code that indicates the success or failure of the function.
Possible return codes include, but are not limited to, the following.
| Return code | Description |
|---|---|
|
The function was successful. |
|
An internal error occurred. |
|
The handle in the hSharedSecret parameter is not valid. |
|
One or more parameters are not valid. |
Remarks
The BCryptBufferDesc structure in the pParameterList parameter can contain more than one of the KDF_SECRET_PREPEND and KDF_SECRET_APPEND parameters. If more than one of these parameters is specified, the parameter values are concatenated in the order in which they are contained in the array before the KDF is called. For example, assume the following parameter values are specified.
BYTE pbValue0[1] = {0x01};
BYTE pbValue1[2] = {0x04, 0x05};
BYTE pbValue2[3] = {0x10, 0x11, 0x12};
BYTE pbValue3[4] = {0x20, 0x21, 0x22, 0x23};
Parameter[0].type = KDF_SECRET_APPEND
Parameter[0].value = pbValue0;
Parameter[0].length = sizeof (pbValue0);
Parameter[1].type = KDF_SECRET_PREPEND
Parameter[1].value = pbValue1;
Parameter[1].length = sizeof (pbValue1);
Parameter[2].type = KDF_SECRET_APPEND
Parameter[2].value = pbValue2;
Parameter[2].length = sizeof (pbValue2);
Parameter[3].type = KDF_SECRET_PREPEND
Parameter[3].value = pbValue3;
Parameter[3].length = sizeof (pbValue3);
If the above parameter values are specified, the concatenated values to the actual KDF are as follows.
Type: KDF_SECRET_PREPEND
Value: {0x04, 0x05, 0x20, 0x21, 0x22, 0x23}, length 6
Type: KDF_SECRET_APPEND
Value: {0x01, 0x10, 0x11, 0x12}, length 4
If the pwszKDF parameter is set to BCRYPT_KDF_RAW_SECRET, The returned secret (unlike the other pwszKDF values) will be encoded in little-endian format. It is important to take note of this when using the raw secret in any other CNG functions, as most of them take in big-endian encoded inputs.
Depending on what processor modes a provider supports, BCryptDeriveKey can be called either from user mode or kernel mode. Kernel mode callers can execute either at PASSIVE_LEVEL IRQL or DISPATCH_LEVEL IRQL. If the current IRQL level is DISPATCH_LEVEL, the handle provided in the hSharedSecret parameter must be located in nonpaged (or locked) memory and must be derived from an algorithm handle returned by a provider that was opened by using the BCRYPT_PROV_DISPATCH flag.
To call this function in kernel mode, use Cng.lib, which is part of the Driver Development Kit (DDK). Windows Server 2008 and Windows Vista: To call this function in kernel mode, use Ksecdd.lib.
Requirements
| Requirement | Value |
|---|---|
| Minimum supported client | Windows Vista [desktop apps | UWP apps] |
| Minimum supported server | Windows Server 2008 [desktop apps | UWP apps] |
| Target Platform | Windows |
| Header | bcrypt.h |
| Library | Bcrypt.lib |
| DLL | Bcrypt.dll |
See also
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