80 lines
3.3 KiB
Go
80 lines
3.3 KiB
Go
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package pac
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import (
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"bytes"
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"gopkg.in/jcmturner/gokrb5.v7/iana/chksumtype"
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"gopkg.in/jcmturner/rpc.v1/mstypes"
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)
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/*
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https://msdn.microsoft.com/en-us/library/cc237955.aspx
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The Key Usage Value MUST be KERB_NON_KERB_CKSUM_SALT (17) [MS-KILE] (section 3.1.5.9).
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Server Signature (SignatureType = 0x00000006)
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https://msdn.microsoft.com/en-us/library/cc237957.aspx
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The KDC will use the long-term key that the KDC shares with the server, so that the server can verify this signature on receiving a PAC.
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The server signature is a keyed hash [RFC4757] of the entire PAC message, with the Signature fields of both PAC_SIGNATURE_DATA structures set to zero.
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The key used to protect the ciphertext part of the response is used.
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The checksum type corresponds to the key unless the key is DES, in which case the KERB_CHECKSUM_HMAC_MD5 key is used.
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The resulting hash value is then placed in the Signature field of the server's PAC_SIGNATURE_DATA structure.
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KDC Signature (SignatureType = 0x00000007)
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https://msdn.microsoft.com/en-us/library/dd357117.aspx
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The KDC will use KDC (krbtgt) key [RFC4120], so that other KDCs can verify this signature on receiving a PAC.
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The KDC signature is a keyed hash [RFC4757] of the Server Signature field in the PAC message.
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The cryptographic system that is used to calculate the checksum depends on which system the KDC supports, as defined below:
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- Supports RC4-HMAC --> KERB_CHECKSUM_HMAC_MD5
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- Does not support RC4-HMAC and supports AES256 --> HMAC_SHA1_96_AES256
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- Does not support RC4-HMAC or AES256-CTS-HMAC-SHA1-96, and supports AES128-CTS-HMAC-SHA1-96 --> HMAC_SHA1_96_AES128
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- Does not support RC4-HMAC, AES128-CTS-HMAC-SHA1-96 or AES256-CTS-HMAC-SHA1-96 --> None. The checksum operation will fail.
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*/
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// SignatureData implements https://msdn.microsoft.com/en-us/library/cc237955.aspx
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type SignatureData struct {
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SignatureType uint32 // A 32-bit unsigned integer value in little-endian format that defines the cryptographic system used to calculate the checksum. This MUST be one of the following checksum types: KERB_CHECKSUM_HMAC_MD5 (signature size = 16), HMAC_SHA1_96_AES128 (signature size = 12), HMAC_SHA1_96_AES256 (signature size = 12).
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Signature []byte // Size depends on the type. See comment above.
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RODCIdentifier uint16 // A 16-bit unsigned integer value in little-endian format that contains the first 16 bits of the key version number ([MS-KILE] section 3.1.5.8) when the KDC is an RODC. When the KDC is not an RODC, this field does not exist.
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}
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// Unmarshal bytes into the SignatureData struct
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func (k *SignatureData) Unmarshal(b []byte) (rb []byte, err error) {
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r := mstypes.NewReader(bytes.NewReader(b))
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k.SignatureType, err = r.Uint32()
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if err != nil {
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return
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}
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var c int
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switch k.SignatureType {
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case chksumtype.KERB_CHECKSUM_HMAC_MD5_UNSIGNED:
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c = 16
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case uint32(chksumtype.HMAC_SHA1_96_AES128):
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c = 12
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case uint32(chksumtype.HMAC_SHA1_96_AES256):
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c = 12
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}
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k.Signature, err = r.ReadBytes(c)
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if err != nil {
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return
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}
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// When the KDC is not an Read Only Domain Controller (RODC), this field does not exist.
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if len(b) >= 4+c+2 {
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k.RODCIdentifier, err = r.Uint16()
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if err != nil {
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return
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}
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}
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// Create bytes with zeroed signature needed for checksum verification
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rb = make([]byte, len(b), len(b))
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copy(rb, b)
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z := make([]byte, len(b), len(b))
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copy(rb[4:4+c], z)
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return
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}
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