ssh_kdf.c File Reference

#include "precomp.h"

Include dependency graph for ssh_kdf.c:

Go to the source code of this file.

Functions
SYMCRYPT_ERROR SYMCRYPT_CALL	SymCryptSshKdfExpandKey (_Out_ PSYMCRYPT_SSHKDF_EXPANDED_KEY pExpandedKey, _In_ PCSYMCRYPT_HASH pHashFunc, _In_reads_(cbKey) PCBYTE pbKey, SIZE_T cbKey)
SYMCRYPT_ERROR SYMCRYPT_CALL	SymCryptSshKdfDerive (_In_ PCSYMCRYPT_SSHKDF_EXPANDED_KEY pExpandedKey, _In_reads_(cbHashValue) PCBYTE pbHashValue, SIZE_T cbHashValue, BYTE label, _In_reads_(cbSessionId) PCBYTE pbSessionId, SIZE_T cbSessionId, _Inout_updates_(cbOutput) PBYTE pbOutput, SIZE_T cbOutput)
SYMCRYPT_ERROR SYMCRYPT_CALL	SymCryptSshKdf (_In_ PCSYMCRYPT_HASH pHashFunc, _In_reads_(cbKey) PCBYTE pbKey, SIZE_T cbKey, _In_reads_(cbHashValue) PCBYTE pbHashValue, SIZE_T cbHashValue, BYTE label, _In_reads_(cbSessionId) PCBYTE pbSessionId, SIZE_T cbSessionId, _Out_writes_(cbOutput) PBYTE pbOutput, SIZE_T cbOutput)

Function Documentation

SymCryptSshKdf()

SYMCRYPT_ERROR SYMCRYPT_CALL SymCryptSshKdf	(	_In_ PCSYMCRYPT_HASH	pHashFunc,
		_In_reads_(cbKey) PCBYTE	pbKey,
		SIZE_T	cbKey,
		_In_reads_(cbHashValue) PCBYTE	pbHashValue,
		SIZE_T	cbHashValue,
		BYTE	label,
		_In_reads_(cbSessionId) PCBYTE	pbSessionId,
		SIZE_T	cbSessionId,
		_Out_writes_(cbOutput) PBYTE	pbOutput,
		SIZE_T	cbOutput
	)

Definition at line 89 of file ssh_kdf.c.

{
    SYMCRYPT_SSHKDF_EXPANDED_KEY expandedKey;
    SYMCRYPT_ERROR  scError = SYMCRYPT_NO_ERROR;
 
    scError = SymCryptSshKdfExpandKey(&expandedKey, pHashFunc, pbKey, cbKey);
 
    if (scError != SYMCRYPT_NO_ERROR)
    {
        goto cleanup;
    }
 
    scError = SymCryptSshKdfDerive(&expandedKey,
                                    pbHashValue, cbHashValue,
                                    label,
                                    pbSessionId, cbSessionId,
                                    pbOutput, cbOutput);
 
 cleanup:
 
    SymCryptWipeKnownSize(&expandedKey, sizeof(expandedKey));
 
    return scError;
}

SymCryptSshKdfDerive()

SYMCRYPT_ERROR SYMCRYPT_CALL SymCryptSshKdfDerive	(	_In_ PCSYMCRYPT_SSHKDF_EXPANDED_KEY	pExpandedKey,
		_In_reads_(cbHashValue) PCBYTE	pbHashValue,
		SIZE_T	cbHashValue,
		BYTE	label,
		_In_reads_(cbSessionId) PCBYTE	pbSessionId,
		SIZE_T	cbSessionId,
		_Inout_updates_(cbOutput) PBYTE	pbOutput,
		SIZE_T	cbOutput
	)

Definition at line 33 of file ssh_kdf.c.

{
    SYMCRYPT_ERROR      scError = SYMCRYPT_NO_ERROR;
    SYMCRYPT_HASH_STATE hashState;
 
    PCBYTE          pcbOutputSave = pbOutput;
    PCSYMCRYPT_HASH pHashFunc = pExpandedKey->pHashFunc;
    SIZE_T          cbHashResultSize = SymCryptHashResultSize(pHashFunc);
 
 
    while (cbOutput > 0)
    {
        SIZE_T cbGeneratedOutput = pbOutput - pcbOutputSave;
 
        SymCryptHashStateCopy(pHashFunc, &pExpandedKey->hashState, &hashState);
        SymCryptHashAppend(pHashFunc, &hashState, pbHashValue, cbHashValue);                // hashState has (K || H)
 
        // label and session ID are appended only in the first iteration
        if (cbGeneratedOutput == 0)
        {
            SymCryptHashAppend(pHashFunc, &hashState, &label, 1);
            SymCryptHashAppend(pHashFunc, &hashState, pbSessionId, cbSessionId);
        }
        else
        {
            // We break the read-once write-once rule here by appending data to a
            // hash computation from pbOutput that was written by SymCryptHashResult()
            // below.
            // Modification of data in pbOutput buffer after it's written and before
            // used again will have uncontrolled disturbances in the hash output and cannot
            // be used to gain knowledge about the secret key.
            SymCryptHashAppend(pHashFunc, &hashState, pcbOutputSave, cbGeneratedOutput);    // hashState has (K || H || K1 .. Ki)
        }
 
        SymCryptHashResult(pHashFunc, &hashState, pbOutput, cbOutput);
 
        SIZE_T bytesCopied = SYMCRYPT_MIN(cbOutput, cbHashResultSize);
 
        pbOutput += bytesCopied;
        cbOutput -= bytesCopied;
    }
 
    return scError;
}

Referenced by SymCryptSshKdf(), SymCryptSshKdfSha256SelfTest(), and SymCryptSshKdfSha512SelfTest().

SymCryptSshKdfExpandKey()

SYMCRYPT_ERROR SYMCRYPT_CALL SymCryptSshKdfExpandKey	(	_Out_ PSYMCRYPT_SSHKDF_EXPANDED_KEY	pExpandedKey,
		_In_ PCSYMCRYPT_HASH	pHashFunc,
		_In_reads_(cbKey) PCBYTE	pbKey,
		SIZE_T	cbKey
	)

Definition at line 17 of file ssh_kdf.c.

{
    pExpandedKey->pHashFunc = pHashFunc;
 
    SymCryptHashInit(pHashFunc, &pExpandedKey->hashState);
    SymCryptHashAppend(pHashFunc, &pExpandedKey->hashState, pbKey, cbKey);
 
    return SYMCRYPT_NO_ERROR;
}

Referenced by SymCryptSshKdf(), SymCryptSshKdfSha256SelfTest(), and SymCryptSshKdfSha512SelfTest().