LND per_commitment_secret

Question

I'm trying to restore per_commitment_secret from channel.backup file (LND). What is the seed? Is the seed saved in channel.backup file?

BOLT #03 per_commitment_secret calculation

generate_from_seed(seed, I):
    P = seed
    for B in 47 down to 0:
        if B set in I:
            flip(B) in P
            P = SHA256(P)
    return P

channel.backup file:

Version: (chanbackup.MultiBackupVersion) 0,
 StaticBackups: ([]dump.BackupSingle) (len=1 cap=1) {
  (dump.BackupSingle) {
   Version: (chanbackup.SingleBackupVersion) 3,
   IsInitiator: (bool) true,
   ChainHash: (string) (len=64) "000000000933ea01ad0ee984209779baaec3ced90fa3f408719526f8d77f4943",
   FundingOutpoint: (string) (len=66) "9e85aa58382ea2ec19cc40abf33e6fdd452e2e8ac641dee91aa2e3f81c1e1d59:0",
   ShortChannelID: (lnwire.ShortChannelID) 2534684:31:0,
   RemoteNodePub: (string) (len=66) "0359faf62fb32f91fa993d253392f5872731799d39c0fe5e4a3f630e2a1b99328e",
   Addresses: ([]net.Addr) (len=1 cap=1) {
    (*net.TCPAddr)(0xc0002fe780)(127.0.0.1:9734)
   },
   Capacity: (btcutil.Amount) 0.00100000 BTC,
   LocalChanCfg: (dump.ChannelConfig) {
    ChannelConstraints: (channeldb.ChannelConstraints) {
     DustLimit: (btcutil.Amount) 0 BTC,
     ChanReserve: (btcutil.Amount) 0 BTC,
     MaxPendingAmount: (lnwire.MilliSatoshi) 0 mSAT,
     MinHTLC: (lnwire.MilliSatoshi) 0 mSAT,
     MaxAcceptedHtlcs: (uint16) 0,
     CsvDelay: (uint16) 144
    },
    MultiSigKey: (dump.KeyDescriptor) {
     Path: (string) (len=17) "m/1017'/1'/0'/0/0",
     PubKey: (string) (len=5) "<nil>"
    },
    RevocationBasePoint: (dump.KeyDescriptor) {
     Path: (string) (len=17) "m/1017'/1'/1'/0/0",
     PubKey: (string) (len=5) "<nil>"
    },
    PaymentBasePoint: (dump.KeyDescriptor) {
     Path: (string) (len=17) "m/1017'/1'/3'/0/0",
     PubKey: (string) (len=5) "<nil>"
    },
    DelayBasePoint: (dump.KeyDescriptor) {
     Path: (string) (len=17) "m/1017'/1'/4'/0/0",
     PubKey: (string) (len=5) "<nil>"
    },
    HtlcBasePoint: (dump.KeyDescriptor) {
     Path: (string) (len=17) "m/1017'/1'/2'/0/0",
     PubKey: (string) (len=5) "<nil>"
    }
   },
   RemoteChanCfg: (dump.ChannelConfig) {
    ChannelConstraints: (channeldb.ChannelConstraints) {
     DustLimit: (btcutil.Amount) 0 BTC,
     ChanReserve: (btcutil.Amount) 0 BTC,
     MaxPendingAmount: (lnwire.MilliSatoshi) 0 mSAT,
     MinHTLC: (lnwire.MilliSatoshi) 0 mSAT,
     MaxAcceptedHtlcs: (uint16) 0,
     CsvDelay: (uint16) 144
    },
    MultiSigKey: (dump.KeyDescriptor) {
     Path: (string) (len=17) "m/1017'/1'/0'/0/0",
     PubKey: (string) (len=66) "03a80d38d0a2d709bae3accc70d50734e71da6cfc9fa005f359d65357d5cf61c8c"
    },
    RevocationBasePoint: (dump.KeyDescriptor) {
     Path: (string) (len=17) "m/1017'/1'/0'/0/0",
     PubKey: (string) (len=66) "020d4faed88bc397b81048dbbc16aeb69aba72b92fd3b2816907c5f37fe2aaa4f4"
    },
    PaymentBasePoint: (dump.KeyDescriptor) {
     Path: (string) (len=17) "m/1017'/1'/0'/0/0",
     PubKey: (string) (len=66) "02f8ef4bbc7c3f520dcb3c57869e73680b41f778b7339dacc185a9a21740254dcd"
    },
    DelayBasePoint: (dump.KeyDescriptor) {
     Path: (string) (len=17) "m/1017'/1'/0'/0/0",
     PubKey: (string) (len=66) "02c314c978afe85f27cf01b4af61059afbb445d03deded4833e2ba8b23ccfd5623"
    },
    HtlcBasePoint: (dump.KeyDescriptor) {
     Path: (string) (len=17) "m/1017'/1'/0'/0/0",
     PubKey: (string) (len=66) "02a085a39448babc5fd4c4a1a4c13362ab5f9e2d51e78afcba056057cc54be3158"
    }
   },
   ShaChainRootDesc: (dump.KeyDescriptor) {
    Path: (string) (len=17) "m/1017'/1'/5'/0/1",
    PubKey: (string) (len=5) "<nil>"
   }
  }
 }
}